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—but also as a virtual cure-all

Claims, purported benefits: Promotes sleep and prevents insomnia; prevents or alleviates jet lag; slows aging; treats or prevents everything from heart disease, cancer, fatigue, anxiety, headaches, and depression to dementia, menopausal symptoms, tinnitus, irritable bowel syndrome, and skin damage from the sun.

Evidence: A 2009 review by the Cochrane Collaboration (which evaluates medical treatments) concluded that supplemental melatonin is effective for preventing or reducing jet lag, though not all studies have had positive results. Melatonin appears to be safe for short-term use, it said, and should be recommended to adult travelers flying across five or more time zones, particularly in an easterly direction.

There’s fairly good evidence for melatonin’s use in treating insomnia in the elderly and enhancing sleep in healthy people. However, it may help you doze off faster but may not help you stay asleep. For all the other proposed benefits, the evidence is conflicting or inconclusive.
The long-term safety and effectiveness of melatonin supplements are unknown. Prolonged use, for instance, may undermine the body’s ability to produce the hormone naturally. Pregnant women and children should not take it.

Bottom line: Consider taking melatonin only for jet lag and insomnia—and only for occasional or short-term use. If you have chronic insomnia or another sleep disorder, consult your doctor, who may refer you to a sleep specialist. Don’t take melatonin in hopes of protecting yourself from cancer or the effects of aging—or for any other health matter not related to sleep. There’s no consensus about which doses, schedule, or formulation of melatonin are best for various sleep disorders.