Exogenous melatonin as a treatment for secondary sleep disorders: A systematic review and meta-analysis

•Determining the effects of exogenous melatonin for secondary sleep disorders.•Melatonin is a physiological indoleamine used for secondary sleep disorders.•Pooled data demonstrate that exogenous melatonin lowers sleep onset latency.•Pooled data demonstrate that exogenous melatonin increases total sleep time.•Pooled data demonstrate that melatonin has little effects on sleep efficiency.