SLEEP-INDUCING EFFECTS OF LOW-DOSES OF MELATONIN INGESTED IN THE EVENING

We previously observed that low oral doses of melatonin given at noon increase blood melatonin concentrations to those normally occurring no cturnally and facilitate sleep onset, as assessed using an involuntary muscle relaxation test. In this study we examined the induction of po lysomnographically recorded sleep by similar doses given later in the evening, close to the times of endogenous melatonin release and habitu al sleep onset. Volunteers received the hormone (oral doses of 0.3 or 1.0 mg) or placebo at 6, 8, or 9 PM. Latencies to sleep onset, to stag e 2 sleep, and to rapid eye movement (REM) sleep were measured polysom nographically. Either dose given at any of the three time points decre ased sleep onset latency and latency to stage 2 sleep. Melatonin did n ot suppress REM sleep or delay its onset. Most volunteers could clearl y distinguish between the effects of melatonin and those of placebo wh en the hormone was tested at 6 or 8 PM. Neither melatonin dose induced ''hangover'' effects, as assessed with mood and performance tests adm inistered on the morning after treatment. These data provide new evide nce that nocturnal melatonin secretion may be involved in physiologic sleep onset and that exogenous melatonin may be useful in treating ins omnia.