What is melatonin? A plain-English guide

Melatonin is a hormone, a chemical messenger, that the brain makes in response to darkness [1]. It helps with the timing of your circadian rhythm, which is your body's 24-hour inner clock, and with sleep [1]. Light at night can block the body's own melatonin [1].

In the US, the FDA regulates melatonin as a dietary supplement, and many kinds are sold over the counter [8].

In several other countries, melatonin is a drug that needs a prescription [1]. In Australia, pharmacists can supply it for two adult uses, and all other melatonin needs a prescription [9].

In Canada, licensed products may be sold to adults 18 and over for occasional sleeplessness, used only when needed, and for jet lag [10]. In the US, melatonin sales rose from $285 million in 2016 to $821 million in 2020 [8].

Does melatonin help you fall asleep faster?

Evidence grade for sleep latency: C, limited. Why this grade

Slightly, on average [2]. A 2005 meta-analysis, which is a study that pools the results of many trials, combined 17 studies with 284 people [2]. Most were in healthy people or people with insomnia only [2]. Compared with a placebo, a dummy pill with nothing active in it, melatonin shortened the time to fall asleep by 4.0 minutes [2]. The authors say the studies were very different in who took part, how sleep was measured and the doses used [2].

But a 2022 meta-analysis of 24 trials in people with long-term insomnia found no clear effect on how fast adults fell asleep [4]. Neither analysis looked at healthy people alone, so it is unclear how well either result applies to healthy adults.

Does melatonin help you sleep longer?

Evidence grade for total sleep time: C, limited. Why this grade

Modestly, on average [2]. In the same 2005 meta-analysis, melatonin added 12.8 minutes of total sleep compared with a placebo [2].

The 2022 review of long-term insomnia trials found no clear effect on total sleep time in adults [4].

Does melatonin help with jet lag?

Evidence grade for jet lag symptoms: B, moderate. Why this grade

Evidence is mixed [3][5]. A 2002 review looked at 10 placebo-controlled trials in airline passengers, airline staff and military personnel [3].

Nine of the 10 trials found less jet lag when melatonin was taken close to bedtime at the destination [3]. These were flights that crossed five or more time zones [3].

A trial followed 257 Norwegian doctors flying home from New York, 6 hours east [5]. It was randomized and double-blind: chance decided who got what, and neither the doctors nor the researchers knew [5]. It compared three melatonin schedules with a placebo and found no significant difference in jet lag scores or hours slept [5].

The review was published in 2002, and many of its results were people's own ratings of how they felt [3].

To see what the grade badges mean, read how we grade evidence.

Table: Doses used in studies (not a recommendation)

These are amounts used in research, not advice; talk to a clinician before trying melatonin.

A 2019 review of 37 trials in people with sleep disorders looked at side effects [7]. The problems reported most often were daytime sleepiness (1.66%), headache (0.74%), dizziness (0.74%) and low body temperature (0.62%) [7]. Very few were judged serious, such as agitation, mood swings, nightmares and palpitations [7]. The review found none in these trials that were life threatening [7].

Most of those trials lasted 4 weeks or less, and only eight were rated "good" for how well they guarded against bias [7]. The authors say the lack of long-term trials limits what is known about long-term use [7].

Health Canada says labels should warn against driving or using machines for 5 hours after use [10]. They should also warn against mixing it with alcohol or other products that cause drowsiness [10].

In a lab test of supplements, melatonin content ranged from 83% below to 478% above the label [6]. More than 71% of products missed the label by more than 10%, and 26% contained serotonin, a related brain chemical [6].

US poison centers recorded 260,435 cases of children and teens swallowing melatonin from 2012 to 2021, and the yearly number rose 530% [8]. The rise came mainly from accidental swallowing by children aged 5 or under [8]. Five children needed a breathing machine, and two died [8].

Health Canada tells people on some medicines to ask a health care practitioner first [10]. These include medicines for seizures or blood pressure, and medicines that suppress the immune system, affect mental state or increase drowsiness [10]. Steroids and blood thinners are on the list too [10]. If you take any of these medicines, talk to your doctor or pharmacist before combining them with melatonin.

• Pregnant or breastfeeding women. Health Canada says not to use melatonin when pregnant or breastfeeding [10]. NCCIH notes there has been little safety research in this group [1].
• Children. In Australia, pharmacists can supply melatonin only for two adult uses, so any product for a child needs a prescription [9]. NCCIH says parents should first speak with a health care provider [1]. It also notes possible, unconfirmed effects on hormonal development [1].
• People with epilepsy or who take blood thinners. The 2002 review cites case reports suggesting harm in epilepsy and with the blood thinner warfarin [3]. NCCIH says people with epilepsy or on blood thinners need medical supervision when using melatonin [1].
• Older adults. NCCIH says melatonin may stay active longer in older people and cause daytime drowsiness [1].
• People with some health conditions. Health Canada asks people with some conditions to check with a health care practitioner first [10]. These include heart and blood vessel, immune, liver or kidney disease, seizure disorders, asthma and diabetes [10].