Melatonin

Several findings below come from people with diagnosed sleep problems, travelers or shift workers rather than healthy adults sleeping normally, and each section names the population. The evidence grading method explains what each grade requires.

Does melatonin help you fall asleep faster?

Slightly, on average [1]. A 2005 meta-analysis (a study that pools results from many trials) combined 17 studies with 284 participants and found melatonin shortened sleep onset latency, the time to fall asleep, by 4.0 minutes compared with placebo [1]. In the 15 studies that enrolled healthy people or people whose only condition was insomnia, the figure was 3.9 minutes [1]. The authors note the studies were highly heterogeneous in who they enrolled, how they measured sleep and the doses used [1].

Larger effects appear in clinical populations [2][5]. A meta-analysis of 19 placebo-controlled trials with 1,683 adults and children diagnosed with primary sleep disorders found melatonin reduced the time to fall asleep by 7.06 minutes [2]; that work was partly funded by Eli Lilly research awards to one author [2]. In adults diagnosed with insomnia disorder, a clinical population, a 2023 meta-analysis of 22 studies of melatonin and ramelteon found prolonged-release melatonin shortened self-rated sleep onset by 6.30 minutes and measured sleep onset by 5.05 minutes [5]. Results in clinical groups may not apply to healthy adults.

Dose and timing seem to matter [3]. A 2024 dose-response meta-analysis of 26 double-blind randomized controlled trials in people with insomnia and healthy volunteers found melatonin gradually reduced sleep onset latency, with the effect peaking at 4 mg/day [3]. Having insomnia, and the time between the dose and the sleep period, both predicted the size of the effect [3].

Evidence is mixed, and results differ by population [4][9][24]. A 2022 meta-analysis of 24 trials in chronic insomnia found melatonin was not significantly effective on sleep onset latency, total sleep time or sleep efficiency in adults [4]. A 2006 meta-analysis of 9 trials with 427 participants whose sleep was restricted, as in jet lag and shift work, found no clear evidence of an effect on the time to fall asleep [9]. A 2014 rapid evidence assessment of 35 randomized trials made weak recommendations for melatonin to help start sleep and for jet lag phase shifts [24].

Does melatonin increase total sleep time?

Modestly, in most analyses [1][2]. The 2005 meta-analysis found melatonin increased total sleep by 12.8 minutes compared with placebo, and by 13.7 minutes in the studies of healthy people or people with insomnia only [1]. In diagnosed primary sleep disorders, total sleep rose by 8.25 minutes, and longer trials using higher doses showed larger effects [2]. Those effects were modest but did not appear to fade with continued use [2].

Small trials in healthy adults point the same way [11][12]. In a double-blind crossover trial of 15 healthy middle-aged volunteers, a single 1.0 mg evening dose increased actual sleep time and sleep efficiency compared with placebo [11]. In a lab study that scheduled sleep at different times of the body clock, 5 mg taken 30 minutes before lights out raised sleep efficiency in 24 healthy adults over 55 during both biological day and night, while 0.3 mg showed only a trend that came from daytime sleep [12]. The authors of that trial note that in young adults melatonin increases sleep duration only when given during the day, when the body's own levels are low [12].

Shift workers are a separate case. A Cochrane review of 15 placebo-controlled trials in 718 shift workers, nine of them on melatonin, found that 1-10 mg of melatonin after a night shift may add about 24 minutes of daytime sleep (seven trials, 263 participants) and 17 minutes of night-time sleep (three trials, 234 participants), both rated low-quality evidence [10]. It found no dose-response effect, and the time to fall asleep may be similar to placebo (low-quality evidence) [10].

Does melatonin improve sleep quality?

Possibly, but the evidence comes from clinical groups [6][2]. A meta-analysis of 23 randomized trials in adults with various diseases found melatonin improved scores on the Pittsburgh Sleep Quality Index, a questionnaire, by 1.24 points [6]. Results varied widely between studies, and the authors found no effect in some disease groups [6]. In people with diagnosed sleep disorders the improvement was 0.67 points [6]. A meta-analysis in primary sleep disorders found a small improvement in overall sleep quality [2]. These are clinical populations; results may not apply to healthy adults.

Does melatonin help with jet lag?

Most trials found less jet lag, but the largest single trial did not [7][8]. A Cochrane review of 10 placebo-controlled trials in airline passengers, airline staff and military personnel found that 9 reported less jet lag when melatonin was taken close to the target bedtime at the destination after flights crossing five or more time zones [7]. The review estimated that about 2 people needed to take melatonin for 1 to benefit, and expected the benefit to be greater the more time zones were crossed and smaller for westward flights [7]. NCCIH summarizes later reviews from 2010 and 2014: four studies with 142 travelers found melatonin may beat placebo for overall jet lag symptoms after eastward flights [25].

Against that, a randomized, double-blind trial of 257 Norwegian physicians returning from New York, a 6-hour eastward flight, found no difference between placebo and three melatonin regimens in jet lag scores, sleep onset or hours slept [8]. A 2006 meta-analysis that pooled jet lag and shift-work trials found no clear evidence of an effect on the time to fall asleep, a different outcome from jet lag symptoms [9]. The Cochrane review was published in 2002, and its outcomes were mostly subjective ratings of jet lag and related symptoms [7].

What the evidence does not show

A 2006 meta-analysis also found no clear evidence of an effect on the time to fall asleep in people with secondary sleep disorders (6 trials, 97 participants) [9]. The rapid evidence assessment of 35 randomized trials made no recommendation for shift workers and called for larger, longer trials with well-characterized products before recommendations for young, healthy adults [24]. A 2026 systematic review found no efficacy data for young children with typical development [23].

After an immediate-release oral dose, melatonin reached its peak level in about 50 minutes, and its half-life (the time to clear half of it) was 45 minutes, according to a systematic review of 22 pharmacokinetic studies [17]. Only about 15% of an oral dose reaches the bloodstream, with a range of 9 to 33% across studies [17]. Age, caffeine, smoking, oral contraceptives and whether a person has eaten all affected these figures [17].

Formulation changes how melatonin behaves in the body [18]. A systematic review of 19 papers covered oral, transdermal, buccal, topical, intravenous and nasogastric forms and found formulation and dose affect pharmacokinetics, but could not recommend specific formulations for specific sleep disorders [18]. Most insomnia trials in the 2023 meta-analysis used prolonged-release melatonin [5], while the Cochrane review found 2 mg slow-release melatonin relatively ineffective for jet lag [7].

Timing findings from studies:

• In the 2024 meta-analysis, the time between dose and sleep predicted the effect, and the authors suggested that a dose 3 hours before the desired bedtime might work better than one 30 minutes before [3].
• In jet lag trials, melatonin taken at the wrong time, early in the day, was liable to cause sleepiness and delay adaptation to local time [7].
• In nine healthy young men given melatonin at 7 a.m., performance on a psychomotor vigilance test was impaired for 6 hours [13].

In trials of people with sleep disorders, most lasting 4 weeks or less, adverse events were few and generally mild to moderate [14]. A systematic review of 37 randomized placebo-controlled trials, with daily doses from 0.15 mg to 12 mg, found the most frequently reported adverse events were daytime sleepiness (1.66%), headache (0.74%), dizziness (0.74%) and hypothermia (0.62%), and identified none that were life threatening [14]. Most of those trials lasted 4 weeks or less, only eight were rated good for risk of bias, and the authors said the scarcity of long-term trials limits conclusions about continuous use [14]. A 2006 meta-analysis of 17 trials with 651 participants found no evidence of adverse effects with use of three months or less [9].

At doses of 10 mg or more, a meta-analysis identified 79 trials with 3,861 adults across a wide range of medical conditions, but only four met its low risk-of-bias criteria [15]. In those four, melatonin caused no detectable increase in serious adverse events but did appear to raise the risk of drowsiness, headache and dizziness, and 29 of the 79 studies did not report adverse events at all [15]. The authors note their confidence limits were very wide because so few suitable data existed [15]. A safety review reports only mild effects such as dizziness, headache, nausea and sleepiness [16]. The NHS lists daytime sleepiness, headaches, stiff or painful joints and nausea or vomiting as side effects [26]. NCCIH notes a possible risk of allergic reactions and says long-term safety information is lacking [25].

Sources advise caution with driving. The NHS advises not driving, cycling or using machinery after taking melatonin [26], and Health Canada's monograph requires labels to say to avoid driving or using machinery for 5 hours [27].

Product quality is a documented problem [20][21]. In a laboratory analysis of supplements, melatonin content ranged from -83% to +478% of the label, more than 71% missed the label claim by over 10%, lot-to-lot content varied by as much as 465%, and 26% contained serotonin [20]. A survey of 110 US products marketed for children, by FDA scientists, found melatonin content from 0% to 667% of the label [21]. NCCIH reports a 2023 study in which 22 of 25 over-the-counter gummy products were inaccurately labeled, with 74 to 347 percent of the stated amount in those containing melatonin [25].

Accidental ingestion by children has risen sharply in the US [22]. US poison centers recorded 260,435 pediatric melatonin ingestions from 2012 to 2021, and the annual number rose 530%, mainly from unintentional ingestions among children aged 5 or under [22]. Among those reported cases, five children required mechanical ventilation and two died [22].

One antidepressant, fluvoxamine, raised the body's own melatonin levels in a small study [19], and the NHS lists it among medicines that may not mix with melatonin [26]. In a randomized-order crossover study of seven healthy volunteers, fluvoxamine increased the body's own melatonin exposure 2.8-fold compared with placebo, while citalopram had no significant effect [19].

Blood thinners and seizure-related risks appear across sources. The Cochrane review notes case reports suggesting harm in people with epilepsy and people taking warfarin [7], and NCCIH says people with epilepsy or taking blood thinners need medical supervision when using melatonin [25]. The NHS lists anti-inflammatory painkillers (NSAIDs) such as ibuprofen, drowsiness-causing medicines such as zopiclone, blood thinners such as warfarin, fluvoxamine, carbamazepine, the combined contraceptive pill and HRT as medicines that may not mix well with melatonin [26]. Health Canada's monograph tells people taking medicines for seizures, blood pressure, immune suppression, mental state or sedation, or steroids or blood thinners, to ask a health care practitioner first, and to avoid alcohol or other products that cause drowsiness [27].

If you take any of these medicines, talk to your doctor or pharmacist before combining them with melatonin.