Melatonin is a hormone, made by the brain's pineal gland that helps regulate your body's internal clock and may help trigger the onset of sleep. Twenty million people tried it in supplement form in 1995 when a host of popular books promoted it as an anti-aging miracle drug. Although there's no evidence to support this claim, it's still a top-seller today.

Melatonin is FDA-approved as a prescription drug for treating sleep disorders in blind people. It helps regulate the body's wake-sleep cycle in people who can't perceive daylight. Some studies found that it may help with sleep-wake disorders in people with mental retardation and autism. Several studies found melatonin may ease insomnia in elderly people with melatonin deficiency. A handful of studies suggest that melatonin is moderately effective for jet lag. In one study, 20 people flew through 12 time zones from New Zealand to London. Those who took melatonin for three days before and after the flight found their energy levels and sleep patterns returned to normal an average of 1.5 days sooner than those who took a placebo (dummy pill). Human evidence suggests that melatonin, along with chemotherapy (anti-cancer drugs) may help treat various cancers, and melatonin may help prevent thrombocytopenia (low platelet levels in the blood) caused by some types of chemotherapy. But melatonin does not seem to help people adjust to rotating shift work and it may actually worsen depression. Although some preliminary studies have shown that melatonin may prolong the lifespan of mice and rats, there is no evidence that taking melatonin supplements will slow the aging process in humans.

The pineal gland is synchronized to the normal 24-hour day, secreting more melatonin at night and less during daylight, so when you travel or work the night shift, it may take several days for your internal clock to adjust. Researchers theorize that you may be able to help the process along by taking a melatonin supplement at times when it would be released naturally according to your new time zone or work schedule, although this can vary from person to person and from day to day. Melatonin secretion also tapers off as you age, possibly explaining why older people often have trouble sleeping. Children under three have the highest amounts; by the time you're 50, you may have about ten times less. No one knows how melatonin induces sleep, but it might have to do with the fact that the hormone is largely responsible for lowering your body temperature at night.

Melatonin can cause headaches, drowsiness, irritability and reduced alertness. We don't know the long-term effects of taking this hormone. Avoid taking it with alcohol or before driving. Women who are pregnant, breast-feeding, or trying to conceive should not take melatonin, since it can decrease their levels of reproductive hormones. Melatonin can increase blood pressure in people taking the blood pressure-lowering medicine Procardia XL (Nifedipine). People with high blood pressure should talk with their doctor before using melatonin. It can stimulate the immune system, so people with autoimmune diseases such as lupus should steer clear of melatonin.

A recent study at the National Jewish Medical and Research Center suggests that melatonin may hamper overnight lung function in people with asthma, so if you have asthma, check with your doctor before using melatonin as a sleep aid.

You can buy chemically synthesized melatonin in capsule or tablet form. But remember, the government doesn't regulate supplements as strictly as it does drugs, so quality and potency can vary from product to product. In rare cases, products may be contaminated with undesirable substances. Ask a pharmacist or naturopath to recommend a reputable brand. If you decide to take it for insomnia, try starting with 0.3 milligrams (mg) at bedtime, gradually increasing the dose up to 3 mg if necessary. For jet lag, a common dose is 5 mg at bedtime for three days before the flight. Keep in mind, melatonin may have widely varying effects depending on your brain chemistry and particular situation.

-- Kate Lee is a former associate editor at Consumer Health Interactive and researcher at Time Inc. Health. She is currently a senior editor at BabyCenter.

References

First published September 3, 1998
Last updated February 14, 2008
Copyright © 1998 Consumer Health Interactive and OneBody, Inc.

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