Melatonin is also found in a variety of foods, although typically in small amounts.^[25] Sources of melatonin that are commonly consumed include:^[26][27]

• Tomatoes:3–114 nanograms per gram (ng/g)^[28][29]
• Walnuts: 3–4 ng/g^[30]
• Cereal (barley, rye): 300–1,000 picograms per gram (pg/g)^[25]
• Strawberries: 1–11 ng/g^[28]
• Night-time milk (functional food product): 10–40 nanograms per milliliter (ng/ml)^[31]
• Wine (from grapes): 50–230 picograms per milliliter (pg/ml)^[28][32]
• Beer (from hops): 52–170 pg/ml^[33]
• Cherries: 2.06–13.46 ng/g^[34]

Yes. The current evidence suggests that melatonin can ease sleep problems associated with jet lag. In situations where external stimuli (sunlight and darkness cycles) and internal stimuli (the internal clock) are not in sync, supplemental melatonin is thought to help re-establish this synchronization. A Cochrane meta-analysis of 10 studies which examined jet lag due to flights traversing five or more time zones found that melatonin taken at the destination bedtime was significantly more effective than placebo at normalizing circadian rhythm and reducing symptoms of jet lag. One of these studies found that doses of 500 mcg (0.5 mg) and 5 mg were similarly effective at reducing jet lag, but participants reported falling asleep faster with the 5 mg dose. The two studies in the meta-analysis reporting individual statistics found that about 17% of participants still experienced severe jet lag after taking melatonin, compared to 67% after taking a placebo.^[23]

Overall, melatonin seems to be helpful to re-establish a healthy circadian rhythm after experiencing jet lag. Interestingly, melatonin could also be used to treat social jet lag (when changes in sleep habits over the weekend disrupt sleep the following week).^[24] Future studies may shed more light on this.

There is currently no compelling evidence that a combination of melatonin and cannabidiol (CBD) improves sleep beyond what can be explained by melatonin alone.

Melatonin and CBD is a popular supplement combo for improving sleep, based on supposedly complementary mechanisms of action (i.e., melatonin promoting sleep onset and CBD theoretically reducing sleep disruption). However, there is little evidence that CBD can improve sleep quality on its own.^[35] But what about when combined with melatonin?

One 4-week randomized controlled trial examined the effect of melatonin and several cannabinoids (including CBD), alone or in combination, on sleep in 1,784 people with sleep disturbances.^[36] Ultimately, taking a combination of CBD, cannabinol (CBN), and melatonin did not clearly reduce sleep disturbances compared to taking melatonin alone. Unfortunately, the lack of placebo group and the inclusion of other cannabinoids (e.g., CBN) limits the generalizability of this study.

It’s possible that taking CBD could increase melatonin levels by inhibiting the enzyme CYP1A2,^[37] which metabolizes melatonin.^[38] In theory, this could mean CBD would make melatonin supplements more potent. However, this has not yet been directly confirmed in humans.

Melatonin supplementation might impact dreams, but it’s hard to say much with certainty. Theoretically, melatonin could promote dreaming by increasing time spent in REM, a primary sleep stage when dreaming occurs. One randomized controlled trial of 22 young adults did find that taking melatonin before bed increased how bizarre participants rated their dreams.^[10] However, aside from this small study, there isn’t much research confirming a dream-enhancing or dream-altering effect of melatonin. In two randomized controlled trials of people with sleep disorders, melatonin supplementation increased time spent in REM but had no obvious effect on the number, intensity, or quality of dreams.^[11] And another study of 30 people with Parkinson’s disease found melatonin supplementation had no apparent effect on the frequency of vivid dreams compared to placebo.^[12]

In some studies, people have stopped taking melatonin due to nightmares, although this is a rare occurrence.^[13][14] It’s also not clear whether the nightmares were caused by melatonin or just happened to occur while the person was taking melatonin. Furthermore, one randomized controlled trial reported no increase in the rates of nightmares with melatonin supplementation.^[15]

Supplementing melatonin doesn’t appear to affect the body’s own production in a negative way. Studies that have administered melatonin at doses of 0.5 mg,^[16] 5.0 mg,^[17] and 50 mg^[16] have found no significant effect on the body's ability to produce a basal level of melatonin. One trial even found that people with insomnia who took 2 mg of melatonin nightly for 6 months had higher natural melatonin synthesis after cessation of the supplement than a historical sample of participants with insomnia who didn't take melatonin.^[18]

In an umbrella review of melatonin supplementation, reported adverse effects appeared uncommon, and were predominantly mild effects such as dizziness, nausea, headaches, and fatigue.^[19] In some studies, doses as high as 75 mg have been used without any serious adverse effects reported.^[20]

It’s worth noting that there are some concerns regarding the safety of melatonin in young children and infants. In a report by the CDC, melatonin ingestion by children resulted in a number of hospitalizations between 2012 and 2021, including at least two infants who ultimately died.^[21]

It’s been suggested that taking melatonin might lower testosterone levels in males. This idea stems in large part from some animal studies in which exogenously-administered melatonin reduced testosterone production.^[39] However, these studies used melatonin exposures of unclear physiological relevance, so their findings should be viewed with caution. Clinical trials on human men, meanwhile, have found that melatonin supplementation of up to 6 mg per night does not reduce testosterone levels.^{[40][41][42][43]}