Origin: A hormone produced by the pineal gland, which is located at the base of the brain.

Dosage: Capsules or tablets; 1 mg to 5 mg at bedtime for insomnia, for no longer than two weeks.

Claims: Aids sleep and treats jet lag.

What we know: A potent antioxidant, melatonin regulates sleep/wake cycles. It appears to treat insomnia and sleep disturbances related to conditions like fibromyalgia and depression. Aspirin and other NSAIDs can decrease melatonin levels.

Studies: A systematic review of studies shows no evidence that melatonin effectively treats sleep disorders or is useful for altered sleep patterns, such as from shift work or jet lag. However, there is evidence that it is safe with short-term use. Another review of studies showed that melatonin reduced the onset of sleep by four minutes and increased the duration of sleep by nearly 13 minutes; another showed that people taking melatonin slept almost 30 minutes longer than people taking placebo.

Higher doses or long-term usage require doctor supervision. Certain medications interact with it, including NSAIDs, beta-blockers, antidepressants, diuretics and vitamin B-12 supplements. Do not take melatonin with alcohol or caffeine, and do not use if you have an autoimmune disease or if you have depression, kidney disease, epilepsy, heart disease or leukemia.