Melatonin

Melatonin is a hormone released by the pineal gland in darkness that signals nighttime to the body and helps set the timing of the sleep-wake cycle.

Production is driven by the circadian clock in the hypothalamus and suppressed by light reaching the retina, so levels rise in the evening, peak in the middle of the night and fall toward morning. Bright light in the evening, including light from screens, delays the rise, which is one reason late-night screen use is associated with later sleep onset. Melatonin is a timing signal rather than a sedative; it tells the body when night is rather than forcing sleep.

In the United States melatonin is sold as a dietary supplement and is widely used for jet lag, shift work and delayed sleep phase, while in many other countries it is available only by prescription. Supplement products vary in actual content relative to the label, and long-term data in children are limited, so its use in young people is usually discussed with a clinician. Melatonin is sometimes combined with cannabinoids in consumer products, but such combinations have not been studied in controlled trials, and cannabinoid research on sleep is early and inconsistent. In animals, veterinarians occasionally use melatonin for specific conditions, and any use in pets should be guided by a veterinarian.