Melatonin is a hormone primarily released at night-time from the pineal gland in mammals. The increase in endogenous melatonin levels is closely associated with many physiological changes. In many cases, similar physiological changes have been found when synthetic exogenous melatonin has been administered to humans. However, the precise nature of melatonin's physiological role and its mechanism of action remain unclear. This review presents a summary of some of the current known physiological effects of melatonin, with a particular focus on the effects in humans. These effects are introduced from an evolutionary perspective. A working hypothesis as to how the diverse physiological effects of melatonin may be produced is also presented, followed by a summary of current knowledge of the toxicology of melatonin. The potential clinical applications of melatonin are also discussed.
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