Effect of melatonin on sleep and rectal temperature of young healthy evening types

The present study assessed in healthy nocturnal juveniles the presence or absence of the hypnotic action of exogenous melatonin and its effect on core temperature by oral administration of exogenous melatonin at a pharmacologically low dose 15 min before going to bed at the normal time. Both sleep latency and the number of instances of waking up after falling asleep tended to decrease, while the amount of Stage 2 sleep increased significantly. However, no hypothermic action regarding the rectal temperature for changes in the circadian phase were observed. According to those results, it is possible that exogenous melatonin has some direct hypnotic action on habitual night sleep, although the extent of this action is considered to be relatively weak.