





Melatonin is a hormone (N-acetyl-5-methoxytryptamine) produced primarily at night by the pineal gland. Its secretion is stimulated by darkness and inhibited by light. Melatonin, an indole, is synthesized from tryptophan by serotonin. The suprachiasmatic nuclei (SCN) of the hypothalamus have melatonin receptors, and melatonin may have a direct effect on the SCN to influence the circadian (sleep) rhythm.