Hormone secreted by the pineal gland of most vertebrates. It appears to be important in regulating sleeping cycles; more is produced at night, and test subjects injected with it become sleepy. Melatonin may be involved in seasonal affective disorder. In mammals other than humans, melatonin may act as a cue to breeding and mating in season.
This entry comes from Encyclopædia Britannica Concise.
For the full entry on melatonin, visit Britannica.com.
Seen & Heard
What made you look up melatonin? Please tell us what you were reading, watching or discussing that led you here.