A hormone made in the brain by the pineal gland, melatonin affects our internal body clock and sleep cycles. Levels rise at night during sleep and fall by day. Melatonin is heavily marketed as a sleeping pill, particularly for older people, and for jet lag.

Claims, purported benefits: Promotes sleep and prevents insomnia; prevents or alleviates jet lag; improves sex life; slows aging; cures migraine, alcoholism, menopausal symptoms.

Evidence: Despite much study, the benefits of melatonin supplements are still unproven. Various dosages have been used in studies, making comparisons difficult. In 2006 a study in the American Journal of Psychiatry, melatonin showed no benefit against jet lag, but a study from Harvard Medical School suggested it might help people whose sleep patterns are disrupted by shift work or by travel across time zones. While most scientists agree that melatonin helps people fall asleep faster, it may not help them stay asleep; plus it may cause a “hangover” effect the next day, similar to some sleeping pills. Chronic supplementation may suppress the body's own production of the hormone.

Bottom line: Before taking melatonin for extended periods of time for sleep-related issues, talk to a physician. Don’t count on melatonin as a remedy for aging, menopausal symptoms, or other medical conditions. Melatonin production does not appear to decline with age as previously thought, and levels may vary naturally across people and according to the time of day. If your body already produces what you need, additional melatonin may not be advisable. Pregnant women and children should never take it. Nobody knows what dosages to take, and there’s no guarantee you are getting what the label says. If you’re flying east, exposing yourself to sunlight the next morning may be just as good as, if not better than, melatonin as a jet lag remedy.