How effective is melatonin for aiding with sleep difficulty?

Question

From Wikipedia:

Taken 30 to 90 minutes before bedtime, melatonin supplementation acts as a mild hypnotic. It causes melatonin levels in the blood to rise earlier than the brain's own production accomplishes. This usage is now commonly used in sleep and relaxation drinks.

Is there any research that supports the claims that melatonin will help you sleep if you have difficulty falling asleep?

Answer 1

Melatonin does not work, or does not work very well in general. Clinically it is prescribed only for delayed sleep phase syndrome.

A comprehensive review of the available studies¹, "Melatonin for Treatment of Sleep Disorders" was made by R. Buscemi et al in 2009. The results are as follows:

Effectiveness

For people without sleeping disorders

The studies are of low-to-moderate quality and evidence clinically insignificant effectiveness with respect to sleep onset time and effectiveness of sleep.

• Melatonin decreased sleep onset latency (SOL) in normal sleepers [...]. The magnitude of this effect appears to be clinically insignificant. There was evidence of possible publication bias in the selection of studies that were analyzed; we found a greater number of studies reporting positive results compared to negative results.
• Melatonin increased sleep efficiency in normal sleepers [...]. The magnitude of this effect appears to be clinically insignificant. There was considerable evidence of possible publication bias in the selection of studies analyzed; we found a greater number of studies reporting positive results compared to negative results.

For people with primary sleep disorders

The studies are of moderate-to-high quality and they indicate are some improvements for people with delayed sleep phase syndrome, but not with people with insomnia:

• [...] SOL was decreased greatly in people with delayed sleep phase syndrome [...]. The magnitude of this effect appears to be clinically significant. SOL was decreased marginally in patients with insomnia [...]. The magnitude of this effect appears to be clinically insignificant. [...] If the analysis is approached using the Fixed Effects Model, melatonin does not have any effect on sleep onset latency in people with primary insomnia.
• Melatonin did not have an effect on sleep efficiency in people with primary sleep disorders; the effects of melatonin did not vary by age, type of primary sleep disorder, dose, or duration of treatment.
• Melatonin did not have an effect on sleep quality, wakefulness after sleep onset (WASO), total sleep time, or percent time spent in REM sleep.

For people with secondary sleeping disorders

Melatonin did not have a clinically significant effect in the reviewed moderate-to-high quality studies.

• Melatonin did not have an effect on sleep onset latency in people with a secondary sleep disorder; [...]
• Melatonin increased sleep efficiency in people with a secondary sleep disorder [...] The magnitude of this effect appears to be clinically insignificant.
• Melatonin did not have an effect on WASO or percent time spent in REM sleep in people with a secondary sleep disorder, but increased total sleep time in this population

Safety

Melatonin seems safe:

The most commonly reported adverse effects of melatonin were nausea (incidence: ~ 1.5 percent), headache (incidence: ~ 7.8 percent), dizziness (incidence: 4.0 percent), and drowsiness (incidence: 20.33 percent); however, these effects were not significant compared to placebo.

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^{1: Buscemi N., Vandermeer B., Pandya R., et al. Melatonin for Treatment of Sleep Disorders. Summary, Evidence Report/Technology Assessment: Number 108. AHRQ Publication Number 05-E002-1, November 2004. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/epcsums/melatsum.htm}