L-theanine is a naturally occurring amino acid, although it isn’t used as a building block for protein synthesis,<a href="#ref-1" id="ref-link-1" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Türközü D, Şanlier N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26192072" target="\_blank" rel="noopener noreferrer"&gt;L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.
&lt;/a&gt;&lt;/p&gt;Crit Rev Food Sci Nutr (2017-May-24)&lt;/div&gt;'>[1]</a><a href="#ref-2" id="ref-link-2" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Li MY, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/35445053" target="\_blank" rel="noopener noreferrer"&gt;L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.
&lt;/a&gt;&lt;/p&gt;Front Nutr (2022)&lt;/div&gt;'>[2]</a> unlike the 20 standard protein-forming amino acids that are synthesized by the genetic code. Several types of <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a>, including black, oolong, and <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">green tea</a>, contain theanine (generally &lt;50 mg per serving).<a href="#ref-3" id="ref-link-3" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Chen Z, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/33475342" target="\_blank" rel="noopener noreferrer"&gt;From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.
&lt;/a&gt;&lt;/p&gt;J Agric Food Chem (2021-Feb-03)&lt;/div&gt;'>[3]</a><a href="#ref-2" id="ref-link-2" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Li MY, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/35445053" target="\_blank" rel="noopener noreferrer"&gt;L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.
&lt;/a&gt;&lt;/p&gt;Front Nutr (2022)&lt;/div&gt;'>[2]</a><a href="#ref-4" id="ref-link-4" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Boros K, Jedlinszki N, Csupor D. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27019564" target="\_blank" rel="noopener noreferrer"&gt;Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples.
&lt;/a&gt;&lt;/p&gt;Pharmacogn Mag (2016)&lt;/div&gt;'>[4]</a> When higher doses are desired, theanine can also be taken as a dietary supplement; the theanine in supplements may be extracted from tea<a href="#ref-3" id="ref-link-3" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Chen Z, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/33475342" target="\_blank" rel="noopener noreferrer"&gt;From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.
&lt;/a&gt;&lt;/p&gt;J Agric Food Chem (2021-Feb-03)&lt;/div&gt;'>[3]</a> or chemically synthesized using bacterial enzymes.<a href="#ref-5" id="ref-link-5" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Mu W, Zhang T, Jiang B. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/25871834" target="\_blank" rel="noopener noreferrer"&gt;An overview of biological production of L-theanine.
&lt;/a&gt;&lt;/p&gt;Biotechnol Adv (2015)&lt;/div&gt;'>[5]</a>

What is L-theanine?

As described above, theanine generally has calming or relaxing effects.<a href="#ref-6" id="ref-link-6" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Williams JL, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31758301" target="\_blank" rel="noopener noreferrer"&gt;The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.
&lt;/a&gt;&lt;/p&gt;Plant Foods Hum Nutr (2020-Mar)&lt;/div&gt;'>[6]</a><a href="#ref-7" id="ref-link-7" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Ai Yoto, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/23107346" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses
&lt;/a&gt;&lt;/p&gt;J Physiol Anthropol (2012 Oct 29)&lt;/div&gt;'>[7]</a><a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a><a href="#ref-9" id="ref-link-9" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27396868" target="\_blank" rel="noopener noreferrer"&gt;Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study
&lt;/a&gt;&lt;/p&gt;Acta Neuropsychiatr (2017 Apr)&lt;/div&gt;'>[9]</a> On the other hand, <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a> is a powerful central nervous system stimulant that is added to some <a href="/foods/energy-drinks/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Energy Drinks&lt;/h6&gt;&lt;p&gt;Energy drinks and shots are beverages that are claimed to increase energy and reduce fatigue. They typically contain caffeine along with a cocktail of other ingredients, including, but not limited to, taurine, glucuronolactone, carnitine, choline, electrolytes, and B vitamins.&lt;/p&gt;&lt;/div&gt;">energy drinks</a> and naturally found in <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a>, <a href="/foods/coffee/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Coffee&lt;/h6&gt;&lt;p&gt;Sometimes referred to as liquid gold, coffee is the most popular source of caffeine in North America (and behind only teas worldwide). Also a source of tons of nutrients, and most recently touted as a source of chlorogenic acid and ferulic acid.&lt;/p&gt;&lt;/div&gt;">coffee</a>, and <a href="/foods/chocolate/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Chocolate&lt;/h6&gt;&lt;p&gt;Chocolate is made from roasted and ground cacao seeds (aka beans) and has been consumed by cultures around the world for centuries. Cacao is thought to have health benefits due to its high content of polyphenols and flavonoids.&lt;/p&gt;&lt;/div&gt;">chocolate</a>. Because <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a> contains both L-theanine and <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a>, some clinical studies have investigated the effects of theanine and caffeine individually and in combination. The current evidence shows that theanine might diminish some of the less desirable physiological effects of caffeine. For example, L-theanine has been shown to blunt both caffeine’s blood-pressure-increasing effects<a href="#ref-20" id="ref-link-20" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Peter J Rogers, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/17891480" target="\_blank" rel="noopener noreferrer"&gt;Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together
&lt;/a&gt;&lt;/p&gt;Psychopharmacology (Berl) (2008 Jan)&lt;/div&gt;'>[20]</a> and its sleep-disrupting effects.<a href="#ref-21" id="ref-link-21" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Baba Y, Takihara T, Okamura N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/37458751" target="\_blank" rel="noopener noreferrer"&gt;Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset.
&lt;/a&gt;&lt;/p&gt;Food Funct (2023-Jul-31)&lt;/div&gt;'>[21]</a> However, theanine does not appear to blunt the beneficial effects of caffeine on cognitive performance. Instead, the above-described beneficial effects of theanine on some aspects of cognitive function,<a href="#ref-10" id="ref-link-10" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Dassanayake TL, Kahathuduwa CN, Weerasinghe VS. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/32777998" target="\_blank" rel="noopener noreferrer"&gt;L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.
&lt;/a&gt;&lt;/p&gt;Nutr Neurosci (2022-Apr)&lt;/div&gt;'>[10]</a><a href="#ref-11" id="ref-link-11" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Yoshitake Baba, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/33751906" target="\_blank" rel="noopener noreferrer"&gt;Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study
&lt;/a&gt;&lt;/p&gt;J Med Food (2021 Apr)&lt;/div&gt;'>[11]</a><a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a><a href="#ref-9" id="ref-link-9" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27396868" target="\_blank" rel="noopener noreferrer"&gt;Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study
&lt;/a&gt;&lt;/p&gt;Acta Neuropsychiatr (2017 Apr)&lt;/div&gt;'>[9]</a> such as <a href="/outcomes/attention/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Attention&lt;/h6&gt;&lt;p&gt;The ability to keep focus on chosen targets, the clinical lack of attention is ADD (or ADHD if hyperactivity exists); Attention and/or Focus may be affected by supplements listed on this page.&lt;/p&gt;&lt;/div&gt;">attention</a>, have been found to be enhanced when caffeine is simultaneously ingested.<a href="#ref-22" id="ref-link-22" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Gail N Owen, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/18681988" target="\_blank" rel="noopener noreferrer"&gt;The combined effects of L-theanine and caffeine on cognitive performance and mood
&lt;/a&gt;&lt;/p&gt;Nutr Neurosci (2008 Aug)&lt;/div&gt;'>[22]</a><a href="#ref-23" id="ref-link-23" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Kahathuduwa CN, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/32753637" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT.
&lt;/a&gt;&lt;/p&gt;Sci Rep (2020-Aug-04)&lt;/div&gt;'>[23]</a><a href="#ref-24" id="ref-link-24" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Chanaka N Kahathuduwa, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/29420994" target="\_blank" rel="noopener noreferrer"&gt;l-Theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging study
&lt;/a&gt;&lt;/p&gt;Nutr Res (2018 Jan)&lt;/div&gt;'>[24]</a><a href="#ref-25" id="ref-link-25" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Chanaka N Kahathuduwa, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26869148" target="\_blank" rel="noopener noreferrer"&gt;Acute effects of theanine, caffeine and theanine-caffeine combination on attention
&lt;/a&gt;&lt;/p&gt;Nutr Neurosci (2017 Jul)&lt;/div&gt;'>[25]</a><a href="#ref-13" id="ref-link-13" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Crystal F Haskell, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/18006208" target="\_blank" rel="noopener noreferrer"&gt;The effects of L-theanine, caffeine and their combination on cognition and mood
&lt;/a&gt;&lt;/p&gt;Biol Psychol (2008 Feb)&lt;/div&gt;'>[13]</a> That said, not all studies have found this synergistic effect.<a href="#ref-26" id="ref-link-26" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;F L Dodd, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/25761837" target="\_blank" rel="noopener noreferrer"&gt;A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood
&lt;/a&gt;&lt;/p&gt;Psychopharmacology (Berl) (2015 Jul)&lt;/div&gt;'>[26]</a><a href="#ref-20" id="ref-link-20" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Peter J Rogers, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/17891480" target="\_blank" rel="noopener noreferrer"&gt;Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together
&lt;/a&gt;&lt;/p&gt;Psychopharmacology (Berl) (2008 Jan)&lt;/div&gt;'>[20]</a> Overall, dose-response studies of L-theanine and <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a> are currently lacking, and the existing studies are small; larger <a href="/glossary/randomized-controlled-trial/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Randomized controlled trial&lt;/h6&gt;&lt;p&gt;Randomized controlled trials (RCTs) are the gold standard for determining whether an intervention actually causes any effects. The use of randomization and control groups helps eliminate the effects of factors other than the treatment being studied.&lt;/p&gt;&lt;/div&gt;">randomized controlled trials</a> are needed to clarify the interaction between theanine and caffeine. Furthermore, the influence of theanine on the exercise-related performance-enhancing effect of caffeine is currently unclear.

What is the effect of combining L-theanine with caffeine?

The current evidence shows that supplementation with L-theanine may help reduce <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a> and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a> in people experiencing acutely stressful situations.<a href="#ref-6" id="ref-link-6" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Williams JL, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31758301" target="\_blank" rel="noopener noreferrer"&gt;The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.
&lt;/a&gt;&lt;/p&gt;Plant Foods Hum Nutr (2020-Mar)&lt;/div&gt;'>[6]</a> Furthermore, L-theanine may also prevent the increase in blood pressure caused by stressful mental tasks.<a href="#ref-7" id="ref-link-7" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Ai Yoto, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/23107346" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses
&lt;/a&gt;&lt;/p&gt;J Physiol Anthropol (2012 Oct 29)&lt;/div&gt;'>[7]</a> Some small studies have also found that L-theanine might lower <a href="/conditions/depression/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Depression&lt;/h6&gt;&lt;p&gt;Depression is a chronic state of low mood often associated with hopelessness, apathy, and fatigue. Unlike sadness, depression is a disorder that persists for weeks or months and interferes with daily life.&lt;/p&gt;&lt;/div&gt;">depression</a> and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a> scores in healthy people and in people with <a href="/conditions/major-depressive-disorder/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Major Depressive Disorder&lt;/h6&gt;&lt;p&gt;MDD, otherwise known as clinical depression or major depression, is a more severe form of depression that may involve feelings of sadness, angry outbursts, a loss of interest in everyday activities, fatigue, feelings of worthlessness, difficulty thinking, and thoughts of suicide.&lt;/p&gt;&lt;/div&gt;">major depressive disorder</a>.<a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a><a href="#ref-9" id="ref-link-9" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27396868" target="\_blank" rel="noopener noreferrer"&gt;Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study
&lt;/a&gt;&lt;/p&gt;Acta Neuropsychiatr (2017 Apr)&lt;/div&gt;'>[9]</a>
Supplementation with L-theanine may also improve some aspects of cognitive function, including <a href="/outcomes/attention/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Attention&lt;/h6&gt;&lt;p&gt;The ability to keep focus on chosen targets, the clinical lack of attention is ADD (or ADHD if hyperactivity exists); Attention and/or Focus may be affected by supplements listed on this page.&lt;/p&gt;&lt;/div&gt;">attention</a>, <a href="/outcomes/executive-function/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Executive Function&lt;/h6&gt;&lt;p&gt;Executive function is a set of cognitive processes and skills related to self-control and behavior management that include working memory, mental flexibility, focus, emotional control, goal-setting, and following directions.&lt;/p&gt;&lt;/div&gt;">executive function</a>, and <a href="/outcomes/memory/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Memory&lt;/h6&gt;&lt;p&gt;The ability to store and recall information. Memory-boosting supplements have mostly been tested in older people, whose memory has degraded, but this page deals with any form of memory and any study population.&lt;/p&gt;&lt;/div&gt;">memory</a>.<a href="#ref-10" id="ref-link-10" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Dassanayake TL, Kahathuduwa CN, Weerasinghe VS. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/32777998" target="\_blank" rel="noopener noreferrer"&gt;L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.
&lt;/a&gt;&lt;/p&gt;Nutr Neurosci (2022-Apr)&lt;/div&gt;'>[10]</a><a href="#ref-11" id="ref-link-11" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Yoshitake Baba, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/33751906" target="\_blank" rel="noopener noreferrer"&gt;Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study
&lt;/a&gt;&lt;/p&gt;J Med Food (2021 Apr)&lt;/div&gt;'>[11]</a><a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a><a href="#ref-9" id="ref-link-9" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27396868" target="\_blank" rel="noopener noreferrer"&gt;Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study
&lt;/a&gt;&lt;/p&gt;Acta Neuropsychiatr (2017 Apr)&lt;/div&gt;'>[9]</a> That said, L-theanine has been found to impair <a href="/outcomes/executive-function/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Executive Function&lt;/h6&gt;&lt;p&gt;Executive function is a set of cognitive processes and skills related to self-control and behavior management that include working memory, mental flexibility, focus, emotional control, goal-setting, and following directions.&lt;/p&gt;&lt;/div&gt;">executive function</a> and lower attentional control when people are in an emotionally aroused state<a href="#ref-12" id="ref-link-12" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Grace E Giles, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/28044450" target="\_blank" rel="noopener noreferrer"&gt;Caffeine and theanine exert opposite effects on attention under emotional arousal
&lt;/a&gt;&lt;/p&gt;Can J Physiol Pharmacol (2017 Jan)&lt;/div&gt;'>[12]</a> or are undertaking stressful mental tasks.<a href="#ref-13" id="ref-link-13" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Crystal F Haskell, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/18006208" target="\_blank" rel="noopener noreferrer"&gt;The effects of L-theanine, caffeine and their combination on cognition and mood
&lt;/a&gt;&lt;/p&gt;Biol Psychol (2008 Feb)&lt;/div&gt;'>[13]</a> 
Further evidence suggests that supplementation with L-theanine might also enhance <a href="/outcomes/sleep-quality/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Sleep Quality&lt;/h6&gt;&lt;p&gt;Sleep quality refers to how restful your sleep is — how well it rejuvenates your mind and body. For you to feel rested in the morning, your sleep must have sufficient duration and quality. Like insufficient sleep duration, poor sleep quality can start a cascade of health issues. You may want to read our ten tips for better sleep.&lt;/p&gt;&lt;/div&gt;">sleep quality</a><a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a><a href="#ref-9" id="ref-link-9" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/27396868" target="\_blank" rel="noopener noreferrer"&gt;Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study
&lt;/a&gt;&lt;/p&gt;Acta Neuropsychiatr (2017 Apr)&lt;/div&gt;'>[9]</a> by promoting a more relaxed state in the brain.<a href="#ref-14" id="ref-link-14" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Theertham P Rao, Motoko Ozeki, Lekh R Juneja. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/25759004" target="\_blank" rel="noopener noreferrer"&gt;In Search of a Safe Natural Sleep Aid
&lt;/a&gt;&lt;/p&gt;J Am Coll Nutr (2015)&lt;/div&gt;'>[14]</a> However, it is important to note that this evidence is derived predominantly from studies of healthy people. There is currently insufficient evidence to make firm conclusions about whether theanine can improve <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a>, <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a>, <a href="/conditions/depression/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Depression&lt;/h6&gt;&lt;p&gt;Depression is a chronic state of low mood often associated with hopelessness, apathy, and fatigue. Unlike sadness, depression is a disorder that persists for weeks or months and interferes with daily life.&lt;/p&gt;&lt;/div&gt;">depression</a>, cognitive function, or <a href="/outcomes/sleep-quality/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Sleep Quality&lt;/h6&gt;&lt;p&gt;Sleep quality refers to how restful your sleep is — how well it rejuvenates your mind and body. For you to feel rested in the morning, your sleep must have sufficient duration and quality. Like insufficient sleep duration, poor sleep quality can start a cascade of health issues. You may want to read our ten tips for better sleep.&lt;/p&gt;&lt;/div&gt;">sleep quality</a> in people with chronic conditions.

What are L-theanine’s main benefits?

The main drawback is that the specific effects of L-theanine have only been tested in a small number of <a href="/glossary/randomized-controlled-trial/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Randomized controlled trial&lt;/h6&gt;&lt;p&gt;Randomized controlled trials (RCTs) are the gold standard for determining whether an intervention actually causes any effects. The use of randomization and control groups helps eliminate the effects of factors other than the treatment being studied.&lt;/p&gt;&lt;/div&gt;">randomized controlled trials</a> which predominantly included healthy people without chronic conditions. Therefore, further high-quality studies are needed to bolster the current evidence.
The clinical evidence cited above shows that supplementation with L-theanine is well-tolerated, with no known reports of adverse effects or toxicity. In rodents, L-theanine has remarkably low toxicity, with one study failing to find any toxic effects when administering up to 4,000 mg of L-theanine per kg of body weight daily for 13 weeks.<a href="#ref-15" id="ref-link-15" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;J F Borzelleca, D Peters, W Hall. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/16759779" target="\_blank" rel="noopener noreferrer"&gt;A 13-week dietary toxicity and toxicokinetic study with l-theanine in rats
&lt;/a&gt;&lt;/p&gt;Food Chem Toxicol (2006 Jul)&lt;/div&gt;'>[15]</a> Additional animal studies have reported similar results with no observed toxicity at remarkably high doses.<a href="#ref-1" id="ref-link-1" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Türközü D, Şanlier N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26192072" target="\_blank" rel="noopener noreferrer"&gt;L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.
&lt;/a&gt;&lt;/p&gt;Crit Rev Food Sci Nutr (2017-May-24)&lt;/div&gt;'>[1]</a> Consequently, it is generally assumed that L-theanine is safe for humans to consume,<a href="#ref-1" id="ref-link-1" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Türközü D, Şanlier N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26192072" target="\_blank" rel="noopener noreferrer"&gt;L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.
&lt;/a&gt;&lt;/p&gt;Crit Rev Food Sci Nutr (2017-May-24)&lt;/div&gt;'>[1]</a> particularly given its long history of consumption in tea. However, specific safety studies in humans are lacking.

What are L-theanine’s main drawbacks?

After consumption, L-theanine can cross the blood-brain barrier<a href="#ref-16" id="ref-link-16" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;T Terashima, J Takido, H Yokogoshi. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/10361674" target="\_blank" rel="noopener noreferrer"&gt;Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine
&lt;/a&gt;&lt;/p&gt;Biosci Biotechnol Biochem (1999 Apr)&lt;/div&gt;'>[16]</a> and affect brain activity by promoting increased alpha-wave activity,<a href="#ref-17" id="ref-link-17" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Manuel Gomez-Ramirez, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/17272967" target="\_blank" rel="noopener noreferrer"&gt;The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine
&lt;/a&gt;&lt;/p&gt;Clin Neuropharmacol (Jan-Feb 2007)&lt;/div&gt;'>[17]</a><a href="#ref-1" id="ref-link-1" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Türközü D, Şanlier N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26192072" target="\_blank" rel="noopener noreferrer"&gt;L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.
&lt;/a&gt;&lt;/p&gt;Crit Rev Food Sci Nutr (2017-May-24)&lt;/div&gt;'>[1]</a><a href="#ref-2" id="ref-link-2" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Li MY, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/35445053" target="\_blank" rel="noopener noreferrer"&gt;L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.
&lt;/a&gt;&lt;/p&gt;Front Nutr (2022)&lt;/div&gt;'>[2]</a> a pattern of brain activity associated with a more relaxed state. This may explain its <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a>-reducing and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a>-reducing effects.<a href="#ref-8" id="ref-link-8" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Shinsuke Hidese, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/31623400" target="\_blank" rel="noopener noreferrer"&gt;Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
&lt;/a&gt;&lt;/p&gt;Nutrients (2019 Oct 3)&lt;/div&gt;'>[8]</a> 
In animal studies, L-theanine has been shown to affect neurotransmitter signaling in the brain by behaving like a <a href="/foods/glutamate/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Glutamate&lt;/h6&gt;&lt;p&gt;Glutamate is a neurotransmitter produced by the body that plays an important role in learning, memory, and brain development. It is an amino acid found in many foods, most commonly as &lt;em&gt;monosodium glutamate&lt;/em&gt; (MSG), including tomatoes, cheese, mushrooms, seaweed, and soy.&lt;/p&gt;&lt;/div&gt;">glutamate</a> reuptake inhibitor as well as a glutamate receptor antagonist.<a href="#ref-18" id="ref-link-18" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Kakuda T, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/12596867" target="\_blank" rel="noopener noreferrer"&gt;Inhibition by theanine of binding of 3HAMPA, 3Hkainate, and 3HMDL 105,519 to glutamate receptors.
&lt;/a&gt;&lt;/p&gt;Biosci Biotechnol Biochem (2002-Dec)&lt;/div&gt;'>[18]</a> Other animal studies demonstrate that L-theanine can also exert neuroprotective effects via its action on gamma-aminobutyric-acid-A (<a href="/supplements/gaba/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;GABA&lt;/h6&gt;&lt;p&gt;GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter. Although supplementation can increase growth hormone levels, the effects are short-lived. Some research has also reported beneficial effects on sleep quality, stress, and mood. However, results have been inconsistent across studies.&lt;/p&gt;&lt;/div&gt;">GABA</a>-A) receptors.<a href="#ref-19" id="ref-link-19" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Egashira N, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/17928735" target="\_blank" rel="noopener noreferrer"&gt;Involvement of GABA(A) receptors in the neuroprotective effect of theanine on focal cerebral ischemia in mice.
&lt;/a&gt;&lt;/p&gt;J Pharmacol Sci (2007-Oct)&lt;/div&gt;'>[19]</a> However, further investigation in humans is needed to confirm these mechanisms of action.<a href="#ref-1" id="ref-link-1" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Türközü D, Şanlier N. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/26192072" target="\_blank" rel="noopener noreferrer"&gt;L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.
&lt;/a&gt;&lt;/p&gt;Crit Rev Food Sci Nutr (2017-May-24)&lt;/div&gt;'>[1]</a><a href="#ref-2" id="ref-link-2" class="ref-link popover" data-tooltip='&lt;div&gt;&lt;p class="mb-3"&gt;Li MY, et al. &lt;a href="https://pubmed.ncbi.nlm.nih.gov/35445053" target="\_blank" rel="noopener noreferrer"&gt;L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.
&lt;/a&gt;&lt;/p&gt;Front Nutr (2022)&lt;/div&gt;'>[2]</a>

How does L-theanine work?

Theanine

Mental Health

L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.

L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.

From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.

Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples.

An overview of biological production of L-theanine.

The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.

Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses

Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial

Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study

L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.

Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study

Caffeine and theanine exert opposite effects on attention under emotional arousal

The effects of L-theanine, caffeine and their combination on cognition and mood

In Search of a Safe Natural Sleep Aid

A 13-week dietary toxicity and toxicokinetic study with l-theanine in rats

Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine

The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine

Inhibition by theanine of binding of 3HAMPA, 3Hkainate, and 3HMDL 105,519 to glutamate receptors.

Involvement of GABA(A) receptors in the neuroprotective effect of theanine on focal cerebral ischemia in mice.

Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together

Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset.

The combined effects of L-theanine and caffeine on cognitive performance and mood

Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT.

l-Theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging study

Acute effects of theanine, caffeine and theanine-caffeine combination on attention

A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood

Nick Milazzo

Natalka Roshak

Thomas Solomon

Bill Willis

Healthy Aging

Memory & Focus

Vegetarians & Vegans

Cognitive Improvement

Executive Function

Working Memory

Calmness

Anxiety Symptoms

Attention

Blood Pressure

Depression Symptoms

Headaches

Prepulse Inhibition

Sleep Quality

Alertness

Cortisol

Fatigue Symptoms

Motor Speed

Numerical Memory

Processing Accuracy

Processing Speed

Reaction Time

Sedation

Sleep Disturbance Signs and Symptoms

Sleep Latency

Subjective Well-Being

Verbal Fluency

Verbal Memory

Stress & Anxiety

Anxiety

Stress Signs and Symptoms

Insomnia Signs and Symptoms

Salivary Alpha-Amylase

Vigor/Activity

Focus & Attention

Heart Rate

Mood & Depression

Mood Improvement

Cardiovascular Health

General Cardiovascular Health

Mental Resilience

Stress

Allergies & Immunity

Immune Health

Interleukin 2

Treg Cells

Granulocyte Count

Interferon Gamma

Interleukin 10

Interleukin 4

Lymphocyte Count

Natural Killer Cell Content

Total Antioxidant Capacity (TAC)

White Blood Cell Count

Schizophrenia

DHEAS

Schizophrenia symptoms

Serum BDNF

Insulin

Serum DHEA

Total cholesterol

Sleep

Sleep Health

Attention Deficit Hyperactivity Disorder

Depression

High Blood Pressure

Aerobic Exercise Performance

Aerobic Exercise Metrics

Blood Lactate (Exercise)

Power Output

Diabetes & Blood Sugar

Liver Health

Metabolic Health

Schizoaffective Disorder

Sleep Disturbances

General Athletic Performance

Effects of l-theanine on attention and reaction time response

Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task

L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance

Effect of L-theanine on sensorimotor gating in healthy human subjects

Effects of Theanine on the Release of Brain Alpha Wave in Adult Males

The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans

L-Theanine reduces psychological and physiological stress responses

The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial

L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomised, placebo-controlled trial

Anti-stress effect of theanine on students during pharmacy practice: positive correlation among salivary α-amylase activity, trait anxiety and subjective stress

The effect of L-theanine supplementation on the immune system of athletes exposed to strenuous physical exercise

The Effect of L-Theanine Incorporated in a Functional Food Product (Mango Sorbet) on Physiological Responses in Healthy Males: A Pilot Randomised Controlled Trial

Serum levels of brain-derived neurotrophic factor and cortisol to sulfate of dehydroepiandrosterone molar ratio associated with clinical response to L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patients

L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder: an 8-week, randomized, double-blind, placebo-controlled, 2-center study

L-theanine is a naturally occurring amino acid, although it isn’t used as a building block for protein synthesis,[reference|url=https://pubmed.ncbi.nlm.nih.gov/26192072|title=L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.|published=2017-May-24|authors=Türközü D, Şanlier N|journal=Crit Rev Food Sci Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/35445053|title=L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.|published=2022|authors=Li MY, Liu HY, Wu DT, Kenaan A, Geng F, Li HB, Gunaratne A, Li H, Gan RY|journal=Front Nutr|] unlike the 20 standard protein-forming amino acids that are synthesized by the genetic code. Several types of <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a>, including black, oolong, and <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">green tea</a>, contain theanine (generally &lt;50 mg per serving).[reference|url=https://pubmed.ncbi.nlm.nih.gov/33475342|title=From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.|published=2021-Feb-03|authors=Chen Z, Wang Z, Yuan H, He N|journal=J Agric Food Chem|][reference|url=https://pubmed.ncbi.nlm.nih.gov/35445053|title=L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.|published=2022|authors=Li MY, Liu HY, Wu DT, Kenaan A, Geng F, Li HB, Gunaratne A, Li H, Gan RY|journal=Front Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27019564|title=Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples.|published=2016|authors=Boros K, Jedlinszki N, Csupor D|journal=Pharmacogn Mag|] When higher doses are desired, theanine can also be taken as a dietary supplement; the theanine in supplements may be extracted from tea[reference|url=https://pubmed.ncbi.nlm.nih.gov/33475342|title=From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production.|published=2021-Feb-03|authors=Chen Z, Wang Z, Yuan H, He N|journal=J Agric Food Chem|] or chemically synthesized using bacterial enzymes.[reference|url=https://pubmed.ncbi.nlm.nih.gov/25871834|title=An overview of biological production of L-theanine.|published=2015|authors=Mu W, Zhang T, Jiang B|journal=Biotechnol Adv|]

As described above, theanine generally has calming or relaxing effects.[reference|url=https://pubmed.ncbi.nlm.nih.gov/31758301|title=The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.|published=2020-Mar|authors=Williams JL, Everett JM, D'Cunha NM, Sergi D, Georgousopoulou EN, Keegan RJ, McKune AJ, Mellor DD, Anstice N, Naumovski N|journal=Plant Foods Hum Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/23107346|title=Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses|published=2012 Oct 29|authors=Ai Yoto, Mao Motoki, Sato Murao, Hidehiko Yokogoshi|journal=J Physiol Anthropol|][reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27396868|title=Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study|published=2017 Apr|authors=Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi Kunugi|journal=Acta Neuropsychiatr|] On the other hand, <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a> is a powerful central nervous system stimulant that is added to some <a href="/foods/energy-drinks/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Energy Drinks&lt;/h6&gt;&lt;p&gt;Energy drinks and shots are beverages that are claimed to increase energy and reduce fatigue. They typically contain caffeine along with a cocktail of other ingredients, including, but not limited to, taurine, glucuronolactone, carnitine, choline, electrolytes, and B vitamins.&lt;/p&gt;&lt;/div&gt;">energy drinks</a> and naturally found in <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a>, <a href="/foods/coffee/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Coffee&lt;/h6&gt;&lt;p&gt;Sometimes referred to as liquid gold, coffee is the most popular source of caffeine in North America (and behind only teas worldwide). Also a source of tons of nutrients, and most recently touted as a source of chlorogenic acid and ferulic acid.&lt;/p&gt;&lt;/div&gt;">coffee</a>, and <a href="/foods/chocolate/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Chocolate&lt;/h6&gt;&lt;p&gt;Chocolate is made from roasted and ground cacao seeds (aka beans) and has been consumed by cultures around the world for centuries. Cacao is thought to have health benefits due to its high content of polyphenols and flavonoids.&lt;/p&gt;&lt;/div&gt;">chocolate</a>. Because <a href="/supplements/tea/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Tea (Camellia sinensis)&lt;/h6&gt;&lt;p&gt;Tea is both the common name of Camellia sinensis and the name of an infusion made with the leaves of this plant. Green tea is unfermented; black tea is fermented; oolong tea is partially fermented.&lt;/p&gt;&lt;/div&gt;">tea</a> contains both L-theanine and <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a>, some clinical studies have investigated the effects of theanine and caffeine individually and in combination. The current evidence shows that theanine might diminish some of the less desirable physiological effects of caffeine. For example, L-theanine has been shown to blunt both caffeine’s blood-pressure-increasing effects[reference|url=https://pubmed.ncbi.nlm.nih.gov/17891480|title=Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together|published=2008 Jan|authors=Peter J Rogers, Jessica E Smith, Susan V Heatherley, C W Pleydell-Pearce|journal=Psychopharmacology (Berl)|] and its sleep-disrupting effects.[reference|url=https://pubmed.ncbi.nlm.nih.gov/37458751|title=Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset.|published=2023-Jul-31|authors=Baba Y, Takihara T, Okamura N|journal=Food Funct|] However, theanine does not appear to blunt the beneficial effects of caffeine on cognitive performance. Instead, the above-described beneficial effects of theanine on some aspects of cognitive function,[reference|url=https://pubmed.ncbi.nlm.nih.gov/32777998|title=L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.|published=2022-Apr|authors=Dassanayake TL, Kahathuduwa CN, Weerasinghe VS|journal=Nutr Neurosci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/33751906|title=Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study|published=2021 Apr|authors=Yoshitake Baba, Shun Inagaki, Sae Nakagawa, Toshiyuki Kaneko, Makoto Kobayashi, Takanobu Takihara|journal=J Med Food|][reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27396868|title=Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study|published=2017 Apr|authors=Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi Kunugi|journal=Acta Neuropsychiatr|] such as <a href="/outcomes/attention/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Attention&lt;/h6&gt;&lt;p&gt;The ability to keep focus on chosen targets, the clinical lack of attention is ADD (or ADHD if hyperactivity exists); Attention and/or Focus may be affected by supplements listed on this page.&lt;/p&gt;&lt;/div&gt;">attention</a>, have been found to be enhanced when caffeine is simultaneously ingested.[reference|url=https://pubmed.ncbi.nlm.nih.gov/18681988|title=The combined effects of L-theanine and caffeine on cognitive performance and mood|published=2008 Aug|authors=Gail N Owen, Holly Parnell, Eveline A De Bruin, Jane A Rycroft|journal=Nutr Neurosci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/32753637|title=Effects of L-theanine-caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT.|published=2020-Aug-04|authors=Kahathuduwa CN, Wakefield S, West BD, Blume J, Dassanayake TL, Weerasinghe VS, Mastergeorge A|journal=Sci Rep|][reference|url=https://pubmed.ncbi.nlm.nih.gov/29420994|title=l-Theanine and caffeine improve target-specific attention to visual stimuli by decreasing mind wandering: a human functional magnetic resonance imaging study|published=2018 Jan|authors=Chanaka N Kahathuduwa, Chathurika S Dhanasekara, Shao-Hua Chin, Tyler Davis, Vajira S Weerasinghe, Tharaka L Dassanayake, Martin Binks|journal=Nutr Res|][reference|url=https://pubmed.ncbi.nlm.nih.gov/26869148|title=Acute effects of theanine, caffeine and theanine-caffeine combination on attention|published=2017 Jul|authors=Chanaka N Kahathuduwa, Tharaka L Dassanayake, A M Tissa Amarakoon, Vajira S Weerasinghe|journal=Nutr Neurosci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/18006208|title=The effects of L-theanine, caffeine and their combination on cognition and mood|published=2008 Feb|authors=Crystal F Haskell, David O Kennedy, Anthea L Milne, Keith A Wesnes, Andrew B Scholey|journal=Biol Psychol|] That said, not all studies have found this synergistic effect.[reference|url=https://pubmed.ncbi.nlm.nih.gov/25761837|title=A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood|published=2015 Jul|authors=F L Dodd, D O Kennedy, L M Riby, C F Haskell-Ramsay|journal=Psychopharmacology (Berl)|][reference|url=https://pubmed.ncbi.nlm.nih.gov/17891480|title=Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together|published=2008 Jan|authors=Peter J Rogers, Jessica E Smith, Susan V Heatherley, C W Pleydell-Pearce|journal=Psychopharmacology (Berl)|] Overall, dose-response studies of L-theanine and <a href="/supplements/caffeine/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Caffeine&lt;/h6&gt;&lt;p&gt;Caffeine is a central nervous system stimulant that can improve sports performance and aspects of cognitive function. Caffeine or caffeine-containing beverages are often taken to help restore alertness and wakefulness or to reduce drowsiness. Despite its side effects, caffeine is safe for most people, and caffeine-containing beverages like tea and coffee are socially acceptable and widely used.&lt;/p&gt;&lt;/div&gt;">caffeine</a> are currently lacking, and the existing studies are small; larger <a href="/glossary/randomized-controlled-trial/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Randomized controlled trial&lt;/h6&gt;&lt;p&gt;Randomized controlled trials (RCTs) are the gold standard for determining whether an intervention actually causes any effects. The use of randomization and control groups helps eliminate the effects of factors other than the treatment being studied.&lt;/p&gt;&lt;/div&gt;">randomized controlled trials</a> are needed to clarify the interaction between theanine and caffeine. Furthermore, the influence of theanine on the exercise-related performance-enhancing effect of caffeine is currently unclear.

The current evidence shows that supplementation with L-theanine may help reduce <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a> and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a> in people experiencing acutely stressful situations.[reference|url=https://pubmed.ncbi.nlm.nih.gov/31758301|title=The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review.|published=2020-Mar|authors=Williams JL, Everett JM, D'Cunha NM, Sergi D, Georgousopoulou EN, Keegan RJ, McKune AJ, Mellor DD, Anstice N, Naumovski N|journal=Plant Foods Hum Nutr|] Furthermore, L-theanine may also prevent the increase in blood pressure caused by stressful mental tasks.[reference|url=https://pubmed.ncbi.nlm.nih.gov/23107346|title=Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses|published=2012 Oct 29|authors=Ai Yoto, Mao Motoki, Sato Murao, Hidehiko Yokogoshi|journal=J Physiol Anthropol|] Some small studies have also found that L-theanine might lower <a href="/conditions/depression/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Depression&lt;/h6&gt;&lt;p&gt;Depression is a chronic state of low mood often associated with hopelessness, apathy, and fatigue. Unlike sadness, depression is a disorder that persists for weeks or months and interferes with daily life.&lt;/p&gt;&lt;/div&gt;">depression</a> and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a> scores in healthy people and in people with <a href="/conditions/major-depressive-disorder/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Major Depressive Disorder&lt;/h6&gt;&lt;p&gt;MDD, otherwise known as clinical depression or major depression, is a more severe form of depression that may involve feelings of sadness, angry outbursts, a loss of interest in everyday activities, fatigue, feelings of worthlessness, difficulty thinking, and thoughts of suicide.&lt;/p&gt;&lt;/div&gt;">major depressive disorder</a>.[reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27396868|title=Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study|published=2017 Apr|authors=Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi Kunugi|journal=Acta Neuropsychiatr|]
Supplementation with L-theanine may also improve some aspects of cognitive function, including <a href="/outcomes/attention/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Attention&lt;/h6&gt;&lt;p&gt;The ability to keep focus on chosen targets, the clinical lack of attention is ADD (or ADHD if hyperactivity exists); Attention and/or Focus may be affected by supplements listed on this page.&lt;/p&gt;&lt;/div&gt;">attention</a>, <a href="/outcomes/executive-function/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Executive Function&lt;/h6&gt;&lt;p&gt;Executive function is a set of cognitive processes and skills related to self-control and behavior management that include working memory, mental flexibility, focus, emotional control, goal-setting, and following directions.&lt;/p&gt;&lt;/div&gt;">executive function</a>, and <a href="/outcomes/memory/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Memory&lt;/h6&gt;&lt;p&gt;The ability to store and recall information. Memory-boosting supplements have mostly been tested in older people, whose memory has degraded, but this page deals with any form of memory and any study population.&lt;/p&gt;&lt;/div&gt;">memory</a>.[reference|url=https://pubmed.ncbi.nlm.nih.gov/32777998|title=L-theanine improves neurophysiological measures of attention in a dose-dependent manner: a double-blind, placebo-controlled, crossover study.|published=2022-Apr|authors=Dassanayake TL, Kahathuduwa CN, Weerasinghe VS|journal=Nutr Neurosci|][reference|url=https://pubmed.ncbi.nlm.nih.gov/33751906|title=Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study|published=2021 Apr|authors=Yoshitake Baba, Shun Inagaki, Sae Nakagawa, Toshiyuki Kaneko, Makoto Kobayashi, Takanobu Takihara|journal=J Med Food|][reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27396868|title=Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study|published=2017 Apr|authors=Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi Kunugi|journal=Acta Neuropsychiatr|] That said, L-theanine has been found to impair <a href="/outcomes/executive-function/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Executive Function&lt;/h6&gt;&lt;p&gt;Executive function is a set of cognitive processes and skills related to self-control and behavior management that include working memory, mental flexibility, focus, emotional control, goal-setting, and following directions.&lt;/p&gt;&lt;/div&gt;">executive function</a> and lower attentional control when people are in an emotionally aroused state[reference|url=https://pubmed.ncbi.nlm.nih.gov/28044450|title=Caffeine and theanine exert opposite effects on attention under emotional arousal|published=2017 Jan|authors=Grace E Giles, Caroline R Mahoney, Tad T Brunyé, Holly A Taylor, Robin B Kanarek|journal=Can J Physiol Pharmacol|] or are undertaking stressful mental tasks.[reference|url=https://pubmed.ncbi.nlm.nih.gov/18006208|title=The effects of L-theanine, caffeine and their combination on cognition and mood|published=2008 Feb|authors=Crystal F Haskell, David O Kennedy, Anthea L Milne, Keith A Wesnes, Andrew B Scholey|journal=Biol Psychol|] 
Further evidence suggests that supplementation with L-theanine might also enhance <a href="/outcomes/sleep-quality/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Sleep Quality&lt;/h6&gt;&lt;p&gt;Sleep quality refers to how restful your sleep is — how well it rejuvenates your mind and body. For you to feel rested in the morning, your sleep must have sufficient duration and quality. Like insufficient sleep duration, poor sleep quality can start a cascade of health issues. You may want to read our ten tips for better sleep.&lt;/p&gt;&lt;/div&gt;">sleep quality</a>[reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|][reference|url=https://pubmed.ncbi.nlm.nih.gov/27396868|title=Effects of chronic l-theanine administration in patients with major depressive disorder: an open-label study|published=2017 Apr|authors=Shinsuke Hidese, Miho Ota, Chisato Wakabayashi, Takamasa Noda, Hayato Ozawa, Tsutomu Okubo, Hiroshi Kunugi|journal=Acta Neuropsychiatr|] by promoting a more relaxed state in the brain.[reference|url=https://pubmed.ncbi.nlm.nih.gov/25759004|title=In Search of a Safe Natural Sleep Aid|published=2015|authors=Theertham P Rao, Motoko Ozeki, Lekh R Juneja|journal=J Am Coll Nutr|] However, it is important to note that this evidence is derived predominantly from studies of healthy people. There is currently insufficient evidence to make firm conclusions about whether theanine can improve <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a>, <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a>, <a href="/conditions/depression/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Depression&lt;/h6&gt;&lt;p&gt;Depression is a chronic state of low mood often associated with hopelessness, apathy, and fatigue. Unlike sadness, depression is a disorder that persists for weeks or months and interferes with daily life.&lt;/p&gt;&lt;/div&gt;">depression</a>, cognitive function, or <a href="/outcomes/sleep-quality/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Sleep Quality&lt;/h6&gt;&lt;p&gt;Sleep quality refers to how restful your sleep is — how well it rejuvenates your mind and body. For you to feel rested in the morning, your sleep must have sufficient duration and quality. Like insufficient sleep duration, poor sleep quality can start a cascade of health issues. You may want to read our ten tips for better sleep.&lt;/p&gt;&lt;/div&gt;">sleep quality</a> in people with chronic conditions.

The main drawback is that the specific effects of L-theanine have only been tested in a small number of <a href="/glossary/randomized-controlled-trial/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Randomized controlled trial&lt;/h6&gt;&lt;p&gt;Randomized controlled trials (RCTs) are the gold standard for determining whether an intervention actually causes any effects. The use of randomization and control groups helps eliminate the effects of factors other than the treatment being studied.&lt;/p&gt;&lt;/div&gt;">randomized controlled trials</a> which predominantly included healthy people without chronic conditions. Therefore, further high-quality studies are needed to bolster the current evidence.
The clinical evidence cited above shows that supplementation with L-theanine is well-tolerated, with no known reports of adverse effects or toxicity. In rodents, L-theanine has remarkably low toxicity, with one study failing to find any toxic effects when administering up to 4,000 mg of L-theanine per kg of body weight daily for 13 weeks.[reference|url=https://pubmed.ncbi.nlm.nih.gov/16759779|title=A 13-week dietary toxicity and toxicokinetic study with l-theanine in rats|published=2006 Jul|authors=J F Borzelleca, D Peters, W Hall|journal=Food Chem Toxicol|] Additional animal studies have reported similar results with no observed toxicity at remarkably high doses.[reference|url=https://pubmed.ncbi.nlm.nih.gov/26192072|title=L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.|published=2017-May-24|authors=Türközü D, Şanlier N|journal=Crit Rev Food Sci Nutr|] Consequently, it is generally assumed that L-theanine is safe for humans to consume,[reference|url=https://pubmed.ncbi.nlm.nih.gov/26192072|title=L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.|published=2017-May-24|authors=Türközü D, Şanlier N|journal=Crit Rev Food Sci Nutr|] particularly given its long history of consumption in tea. However, specific safety studies in humans are lacking.

After consumption, L-theanine can cross the blood-brain barrier[reference|url=https://pubmed.ncbi.nlm.nih.gov/10361674|title=Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine|published=1999 Apr|authors=T Terashima, J Takido, H Yokogoshi|journal=Biosci Biotechnol Biochem|] and affect brain activity by promoting increased alpha-wave activity,[reference|url=https://pubmed.ncbi.nlm.nih.gov/17272967|title=The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine|published=Jan-Feb 2007|authors=Manuel Gomez-Ramirez, Beth A Higgins, Jane A Rycroft, Gail N Owen, Jeannette Mahoney, Marina Shpaner, John J Foxe|journal=Clin Neuropharmacol|][reference|url=https://pubmed.ncbi.nlm.nih.gov/26192072|title=L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.|published=2017-May-24|authors=Türközü D, Şanlier N|journal=Crit Rev Food Sci Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/35445053|title=L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.|published=2022|authors=Li MY, Liu HY, Wu DT, Kenaan A, Geng F, Li HB, Gunaratne A, Li H, Gan RY|journal=Front Nutr|] a pattern of brain activity associated with a more relaxed state. This may explain its <a href="/conditions/stress/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Stress&lt;/h6&gt;&lt;p&gt;Stress (particularly distress) is excessive stimulation of the body's resources that eventually leads to negative symptoms such as fatigue or depression. Several supplements, such as adaptogens, are thought to reduce the development of stress.&lt;/p&gt;&lt;/div&gt;">stress</a>-reducing and <a href="/conditions/anxiety/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Anxiety&lt;/h6&gt;&lt;p&gt;Anxiety is characterized by excessive tension and worry. Unlike fear, it is persistent and future oriented. There are many types of anxiety disorders, including generalized anxiety, social anxiety, phobias, and panic disorder.&lt;/p&gt;&lt;/div&gt;">anxiety</a>-reducing effects.[reference|url=https://pubmed.ncbi.nlm.nih.gov/31623400|title=Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial|published=2019 Oct 3|authors=Shinsuke Hidese, Shintaro Ogawa, Miho Ota, Ikki Ishida, Zenta Yasukawa, Makoto Ozeki, Hiroshi Kunugi|journal=Nutrients|] 
In animal studies, L-theanine has been shown to affect neurotransmitter signaling in the brain by behaving like a <a href="/foods/glutamate/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;Glutamate&lt;/h6&gt;&lt;p&gt;Glutamate is a neurotransmitter produced by the body that plays an important role in learning, memory, and brain development. It is an amino acid found in many foods, most commonly as &lt;em&gt;monosodium glutamate&lt;/em&gt; (MSG), including tomatoes, cheese, mushrooms, seaweed, and soy.&lt;/p&gt;&lt;/div&gt;">glutamate</a> reuptake inhibitor as well as a glutamate receptor antagonist.[reference|url=https://pubmed.ncbi.nlm.nih.gov/12596867|title=Inhibition by theanine of binding of 3HAMPA, 3Hkainate, and 3HMDL 105,519 to glutamate receptors.|published=2002-Dec|authors=Kakuda T, Nozawa A, Sugimoto A, Niino H|journal=Biosci Biotechnol Biochem|] Other animal studies demonstrate that L-theanine can also exert neuroprotective effects via its action on gamma-aminobutyric-acid-A (<a href="/supplements/gaba/" class="popover" data-tooltip="&lt;div&gt;&lt;h6&gt;GABA&lt;/h6&gt;&lt;p&gt;GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter. Although supplementation can increase growth hormone levels, the effects are short-lived. Some research has also reported beneficial effects on sleep quality, stress, and mood. However, results have been inconsistent across studies.&lt;/p&gt;&lt;/div&gt;">GABA</a>-A) receptors.[reference|url=https://pubmed.ncbi.nlm.nih.gov/17928735|title=Involvement of GABA(A) receptors in the neuroprotective effect of theanine on focal cerebral ischemia in mice.|published=2007-Oct|authors=Egashira N, Hayakawa K, Osajima M, Mishima K, Iwasaki K, Oishi R, Fujiwara M|journal=J Pharmacol Sci|] However, further investigation in humans is needed to confirm these mechanisms of action.[reference|url=https://pubmed.ncbi.nlm.nih.gov/26192072|title=L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety.|published=2017-May-24|authors=Türközü D, Şanlier N|journal=Crit Rev Food Sci Nutr|][reference|url=https://pubmed.ncbi.nlm.nih.gov/35445053|title=L-Theanine: A Unique Functional Amino Acid in Tea ( L.) With Multiple Health Benefits and Food Applications.|published=2022|authors=Li MY, Liu HY, Wu DT, Kenaan A, Geng F, Li HB, Gunaratne A, Li H, Gan RY|journal=Front Nutr|]

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