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★★★Well replicated — this finding’s sources average out to meta-analyses, systematic reviews or high-powered trials.
Melatonin's side effects were mostly mild in trials up to 29 weeks
Across 37 sleep trials at up to 12 mg a day, the commonest was daytime sleepiness, at 1.66%. Palpitations appeared rarely and nothing was life-threatening.
What the study found
Rare palpitations, nothing life-threatening, in 37 melatonin trials
Over trials of up to 29 weeks at 0.15 to 12 mg of melatonin a day, the commonest side effects were daytime sleepiness (1.66%), headache and dizziness (0.74% each). Palpitations appeared rarely and nothing was life-threatening. Across those months, melatonin's harms were mostly mild.
The caveat · Mixes children's and adults' trials
The review mixed trials in children and adults, so the rates are not adults' alone. Only 8 of the 37 trials were rated good quality, and 13 were rated poor. No rate was given for palpitations.