Nine randomised controlled trials (RCTs) were included (n=183): seven crossover and two parallel-group RCTs. Crossover studies incorporated a one-week wash-out period between treatment periods. Sample size ranged from 6 to 51. Downs and Black quality scores ranged from 19 to 31 out of a maximum 32 (mean 25.28).
Compared to placebo, melatonin was associated with a statistically significant reduction in sleep latency (WMD -33.8 minutes, 95% CI -42.97 to -24.70, p<0.001; seven studies), a significantly reduced mean number of wakes per night (WMD -0.16, 95% CI -0.30 to 0.02, p=0.024; eight studies) and significantly increased total sleep time (WMD 0.83 hours, 95% CI 0.57 to 1.08, p<0.001; seven studies).
Funnel plots and statistical tests showed no evidence of publication bias. Galbraith plots apparently showed some evidence of statistical heterogeneity, but Τ2 was zero.
Adverse effects: Four studies specified adverse effects. The authors stated that adverse effects were minor, with a similar incidence in melatonin and placebo phases.