A popular dietary supplement, melatonin used to be promoted simply as a way to treat insomnia and prevent jet lag. No more.

Jet Lag Image - Masterfile

Now, among the purported effects of melatonin, the supplement is touted to treat or prevent everything from fatigue, anxiety, headaches, and depression to dementia, tinnitus, irritable bowel syndrome, and skin damage from the sun. Not to mention heart disease and cancer, as well as menopausal symptoms and all the other signs of aging. There are even melatonin-based drinks like iChill and Dream Water that are supposed to help you relax.

But are these effects of melatonin real? Anything that's marketed as a cure-all should set off warning bells.

Melatonin: The Darkness Hormone

Melatonin is a hormone produced by the brain's pineal gland; it is also found in some edible plants. It has been called the "darkness hormone" (in contrast to vitamin D, the "sunshine hormone") because it is secreted at night; exposure to light suppresses it. Since melatonin affects circadian rhythms—that is, our internal body clock and sleep/wake cycle—and promotes drowsiness, it has long been used as a sleeping aid. In fact, one prescription sleeping pill, ramelteon (Rozerem), works by mimicking the effects of melatonin in the body.

Recent research on isolated cells and lab animals has shown that melatonin has antioxidant, anti-inflammatory, immunological, and potential anti-cancer effects. Such findings don’t mean, of course, that these effects of melatonin extend to people to any significant degree.

How Aging Affects Melatonin Production in the Body

Melatonin production tends to decline as people age. Some researchers have suggested that various age-related changes and conditions (such as declining immunity, cognitive losses, and sleep disturbances) are due at least in part to this drop in melatonin.

Marketers often use the notion that declining melatonin levels need to be replaced as a selling point for supplements—similar to the way estrogen "replacement" therapy was once promoted as a way to prevent chronic disease and keep women feeling young. But can you bring back the desired effects of melatonin?

The truth is many compounds produced by the body decline with age. And even if you replaced them, that wouldn't necessarily help keep you healthy or prevent the effects of aging—and it wouldn’t necessarily be without risk.

Some Well-supported Claims About the Effects of Melatonin

A 2009 review by the Cochrane Collaboration (which evaluates medical treatments) concluded that the effects of melatonin supplementation include 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.

The Natural Standard (which reviews complementary and alternative treatments) has also found "strong" evidence for melatonin’s use for jet lag, as well as some good evidence for its use in treating insomnia in the elderly and enhancing sleep in healthy people. But for all the other supposed effects of melatonin, it said, the evidence is conflicting or inconclusive.

Cancer-Preventing Effects of Melatonin are a Big Maybe

In recent years scientists have been investigating the possible effects of melatonin and nighttime light exposure on the risk of cancer. Studies have found that suppressing melatonin in lab animals—usually by exposing them to light at night—can promote cancer. This has raised concerns that people who have circadian rhythm disruptions because of shift work (such as nurses and flight attendants who work at night and/or in changeable shifts) may be at increased risk for cancer. But the findings have been far from clear, and more research needs to be done to determine if, and how, such disruptions increase cancer risk, as well as what the effects of melatonin might possibly be. Thus far, there's no evidence that melatonin supplements reduce the risk of cancer.

Is It Safe to Use Melatonin Long Term?

The long-term safety and effectiveness of melatonin supplements are unknown. Plus, the side effects of melatonin still need to be fully elucidated. Prolonged use, for instance, may undermine the body's ability to produce the hormone naturally. Hormones are powerful substances that, even in small doses, can produce unexpected and unwanted results, as was seen with estrogen therapy. In most other countries, melatonin's availability is restricted; at least one formulation has been approved for prescription use in Europe, Australia, and Israel for up to three months of use in people over 55.

Various adverse effects from melatonin have been reported, including high blood sugar, breast swelling in men, decreased sperm count, gastrointestinal irritation, sleepwalking, and dizziness. Melatonin may interact with other hormones, so pregnant women, those trying to become pregnant, and children shouldn’t take it. If you have a chronic disease, such as diabetes, liver or kidney disease, clinical depression, or an immune disorder, consult your doctor before taking melatonin.

For some people, the effects of melatonin are curious: melatonin helps them doze off faster but doesn't help them stay asleep.

What Are the Effects of Melatonin on Sleep?

  • Like other sleeping pills, melatonin can produce a "hangover effect" and drowsiness the next day. That's risky if you are driving or operating machinery.
  • There's no consensus about which doses, schedule, or formulation of melatonin are best for various sleep disorders, according to a report in Sleep Medicine Reviews in 2009. It pointed out that some studies show that the effects of melatonin may not even be clearly related to dose. In any case, as with other dietary supplements, you can't even be sure that the dose listed on the label is accurate.
  • Though melatonin is found in some edible plants—including rice, bananas, cherries, and grapes—it's unclear how much consuming these foods raises blood levels of melatonin and what the magnitude of the effects of melatonin might be.

A small recent study in the Journal of Medicinal Food found that tart cherry juice, compared to a placebo drink, helped older people with insomnia sleep a little better. The subjects drank 16 ounces a day (the equivalent of 100 cherries), supplying about 250 calories. That's a lot of juice and calories for a "modest" effect.

Before Taking Melatonin

  • Consider taking melatonin supplements 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.


Originally published in The University of California, Berkeley Wellness Letter (January 2011)

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 28 Apr 2011

Last Modified: 23 Jan 2015