THC has been proposed as a potentially useful compound in the management of dementia, particularly for behavioral symptoms like aggression, agitation, trouble sleeping, wandering, and poor dietary intake. Further, some research in rodents has found that activation of cannabinoid receptor 2 (CB2) receptors in immune cells in the brain may reduce neuroinflammation, oxidative stress, and the formation of the amyloid plaques characteristic of Alzheimer’s disease.^[32]

A handful of randomized controlled trials, uncontrolled trials, and case reports have suggested that THC and its analogs might improve some of the behavioral and psychological symptoms of dementia, most notably aggression and agitation. THC was usually provided at low dosages (≤5 mg daily) and was reportedly well-tolerated, aside from sedation.^[32][33]

However, all studies have been small and short in duration, and the safety of THC (including its effect on cognitive function) has not been adequately explored in this population. Research is fairly consistent in showing that even a single dose of THC can cause short-term impairments in working memory and executive function in an otherwise healthy person, which raises the concern of how it might affect cognition in an older adult with dementia.^[34]

Overall, the current evidence of benefit is weak, and, paired with the known negative effects of THC on cognition, using THC in this context seems ill-advised at this time.

THC is well known for its appetite-stimulating effects, more commonly referred to as “the munchies”. While polishing off an entire bag of chips may not be in everyone's best interest, increasing caloric intake may be desired in certain medical conditions where drastic weight loss is contributing to the deterioration of health.

Human immunodeficiency virus (HIV), cancer, and anorexia nervosa can all lead to potentially deleterious weight loss. Preliminary research seems to suggest that THC can stimulate appetite in these populations, leading to increased food intake and potential weight gain; however, the evidence is relatively weak, and it’s not clear whether this translates to improvements in health outcomes or quality of life.^[8][14][5]

If you’re interested in learning more, check out our article The Science Behind Munchies: Cannabis And Your Appetite

Our endocannabinoid system is involved in the regulation of emotional and stress responses as well as the consolidation and extinction (forgetting) of memories. Further, some evidence suggests that post-traumatic stress disorder (PTSD) may alter the function of the endocannabinoid system.^[35] This has led to the question of whether THC may have a role in the management of PTSD.

Preliminary research has been somewhat promising, although studies have tended to be small, and only a few have been randomized controlled trials. THC may reduce some of the symptoms of PTSD, including a reduction in nightmares, improved sleep, and an increased sense of well-being.^[35] Studies looking at brain function have also suggested that THC may reduce the reactivity of the amygdala (the part of the brain involved in detecting danger) in response to a threat, which may help facilitate emotional regulation and fear reduction.^[36]

It’s important to consider that people with PTSD have an increased risk of substance use disorder (including cannabis use disorder) and may have other psychiatric conditions that could be worsened through THC exposure.^[37] Additionally, an observational study suggested that over time, THC may worsen trauma-related intrusive thoughts.^[38]

Clearly, more research is needed to better understand the potential benefits (and risks) of THC in PTSD.

THC, and cannabis in general, are often reported (anecdotally) to improve sleep. In a survey of Canadians who used cannabis for therapeutic purposes, 85% of people reported using cannabis for sleep, making it the most frequently reported use.^[39] Despite this, the research is limited, and the results have been fairly mixed.

THC may improve self-reported sleep quality, including reducing the time to fall asleep (sleep latency) and increasing total sleep time. These effects have been the most notable in people with chronic pain but appear less consistently in other populations.^[40][11] However, there seems to be a mismatch between subjective and objective measurements of sleep quality. In studies that have monitored brainwave activity, THC has been found to suppress rapid eye movement (REM) sleep and possibly slow-wave sleep (which is important for memory consolidation) with chronic use, and some studies have found increases in sleep latency rather than the self-reported decreases.^[40][41][42]

Data collected in the United States from 2016 to 2017 found that around 7% of pregnant women reported using cannabis during pregnancy.^[19] While potentially helpful for nausea and vomiting, THC is not recommended during pregnancy for several reasons.

The cannabinoid receptor 1 (CB1) receptors that THC exerts its actions through are found in the fetus as early as the first trimester and play an important role in the development of the nervous system. This, paired with the knowledge that THC crosses the placenta, raises a legitimate concern about the effects early exposure to THC might have on the developing fetus.^[20]

Observational research suggests that exposure to cannabis during pregnancy may be associated with an increased risk of low birth weight, preterm birth (<37 weeks gestation), small for gestational age diagnosis, and admission to the neonatal intensive care unit (NICU).^[21][20] Whether cannabis exposure during pregnancy affects cognitive processes into childhood is poorly researched. However, some preliminary research suggests it may be associated with impairments in attention and a higher likelihood of aggressive and hyperactive behaviors.^[20]

Regarding lactation, THC has been found to concentrate in breast milk, meaning levels of THC in breast milk can accumulate and exceed plasma levels in people who use cannabis regularly.^[22] Regular use of THC may also affect the composition of breast milk.^[23] Still, how THC exposure through breast milk affects an infant in both the short-term and the long-term is poorly researched.^[24]

Observational studies have consistently shown that recreational cannabis use is associated with an increased risk of psychosis — a condition that can cause delusions and hallucinations, making it challenging to determine what is reality. While observational studies can’t determine whether cannabis causes psychosis (as opposed to psychosis leading people to use cannabis), the current evidence seems to suggest it. If so, THC is the likely culprit.

Multiple longitudinal cohort studies around the world have generated similar results, finding a dose-dependent relationship between cannabis use and the development of psychosis, even when controlling for multiple confounders.^{[25][26][27][28][29]} Additionally, the relationship does not seem to be influenced by whether someone has a history of psychotic symptoms.^[30]

The risk of psychosis seems to be influenced by a number of factors, including the use of higher-potency cannabis (containing higher doses of THC), exposure early in life (i.e., adolescence), long-term cannabis use, and a family or personal history of psychosis.^[17][25] Interestingly, a gene variant that influences how dopamine is metabolized in the brain has been linked to an increased risk of psychosis in adolescents exposed to cannabis.^[31]