A systematic review 1 including 30 studies with a total of 1,449 subjects was abstracted in DARE. Melatonin decreased sleep onset latency (SOL) in people with a primary sleep disorder (WMD -10.7 minutes, 95% confidence interval, CI: -17.6 to -3.7), though studies were heterogeneous. SOL was decreased greatly in people with delayed sleep phase syndrome (WMD -38.8 minutes, 95% CI: -50.3 to -27.3). SOL was decreased marginally in patients with insomnia, but the size of this effect appeared to be clinically insignificant (WMD -4.3 minutes, 95% CI: -8.4 to -0.1). The effects of melatonin did not vary with the dose or duration of treatment. Melatonin did not have an effect on sleep efficiency, sleep quality, wakefulness after sleep onset, total sleep time, or percentage time spent in REM sleep. Melatonin was safe in the short term.
Comment: The quality of evidence is downgraded by inconsistency (variability in results across studies).
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