In the sleep medicine field, melatonin has been investigated for the treatment of phase shift sleep disorders (such as jet lag syndrome), some parasomnias and primary insomnia, the latter of which is discussed in this article.
The sleep–wake cycle
The human sleep–wake cycle is driven by two primary physiological processes: the homeostatic drive (likely to be neurochemically mediated and dependent on the duration of prior wakefulness and the quality and duration of prior sleep episodes) and the circadian process.
Endogenous melatonin secretion by the pineal gland during the dark/night phase of the sleep–wake cycle is under direction from the circadian pacemaker (the suprachiasmatic nucleus) in the anterior hypothalamus and is closely associated with the human endogenous rhythm of sleep propensity. Other factors such as core body temperature are also driven by this circadian influence and are associated with sleep propensity.