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Other common name(s): none

Scientific/medical name(s): N-acetyl-5-methoxytryptamine


Melatonin is a hormone produced naturally by the pineal gland-- a pea-sized gland located just beneath the center of the brain-- in response to darkness. Melatonin is also available as a man-made supplement.


Research suggests that the melatonin made by the body plays a large role in the daily rhythms of sleeping and waking. Some recent studies have found that people who work night shifts may be at increased risk for cancer, which could be linked to melatonin levels in the body. Study results regarding the effect of melatonin supplements on survival and quality of life in people with cancer have been mixed, and further research in this area is needed.

How is it promoted for use?

There is some evidence that melatonin may have a role in the regulation of daily body cycles, sleep patterns, mood, and reproduction. Possible effects on tumor growth and aging are also under study.

Melatonin is promoted mainly as a sleep aid. Its production in the body may decrease with age, which, according to proponents, may explain why many older people have trouble sleeping. Melatonin is also promoted to help people adjust to odd or irregular work schedules and to counter the effects of jet lag, as it may restore normal sleeping and waking schedules. Some practitioners also believe that melatonin influences hormones in the body that regulate reproduction, the timing of ovulation, and aging. It is sometimes promoted to prevent Alzheimer disease and is often sold as an anti-aging hormone.

Proponents also claim that melatonin is a powerful anti-oxidant, a compound that blocks the action of free radicals, activated oxygen molecules that can damage cells. Because of melatonin's suspected antioxidant properties, some believe it may suppress the growth of some types of cancer cells, especially when combined with certain anti-cancer drugs. Some supporters suggest that melatonin may also stimulate a type of white blood cell called natural killer cells, which attack tumors.

Others suggest that melatonin levels and daily body cycles are abnormal in some people with cancer and that melatonin supplements may help them sleep at night. There are also claims that melatonin may decrease the toxic effects of radiation therapy and chemotherapy.

What does it involve?

Melatonin is sold as a supplement and is available in drugstores, health food stores, and over the Internet. There are no widely accepted recommendations for dosage or duration of use. Melatonin can also be found in many foods, such as milk, peanuts, almonds, turkey, and chicken, but in such small amounts that one would have to eat very large volumes to obtain a measurable dose.

What is the history behind it?

The existence of the pineal gland has been known for thousands of years, although its function remained a mystery until the late 20th century. In the 1600s, the French philosopher René Descartes called the pineal gland "the seat of the soul," because many people believed emotions originated there.

Researchers at Yale University first discovered melatonin and its connection to the pineal gland in the late 1950s. Its link to sleep and hormonal influences and its possible link to cancer have been studied since that time. Melatonin became available as a dietary supplement in the 1990s.

What is the evidence?

Some recent research has suggested that low melatonin levels in the body may be linked to a higher risk of certain types of cancer. For example, a few studies have found that women who work night shifts for many years (and therefore would be expected to have lower levels of melatonin) seem to have a slightly higher risk of breast and colorectal cancer. Even if this research is confirmed, however, it does not necessarily mean that melatonin supplements can lower cancer risk.

Melatonin has been shown to slow or stop the growth of several types of cancer cells when studied in the laboratory. Whether this same effect occurs in the body is unknown.

Several studies have looked at the use of melatonin to treat cancer. Melatonin has been used alone and combined with chemotherapy, radiation therapy, hormone therapy (such as tamoxifen), or immunotherapy (such as interleukin-2) in a number of studies involving different types of cancer. Some of the studies have suggested that melatonin may extend survival and improve quality of life for patients with certain types of untreatable cancers such as advanced lung cancer and melanoma. Some studies reported that a small number of cancers went into total or partial remission, while other studies indicated that melatonin caused little or no response in tumors.

In a 2005 clinical trial looking at cancer-related weight loss (cachexia), melatonin was compared to fish oil in a small group of patients with advanced intestinal cancer. Although neither group gained weight on these substances, three of the eleven patients in the melatonin group did not lose more weight over the 4 week trial period. However, this study was limited by its small size and short period of follow up, and other factors may have accounted for the more stable weight in these patients.

Most of the studies reporting positive results from melatonin were small and conducted by the same group of Italian researchers. Before the results are widely accepted, they will need to be confirmed in larger studies at other centers.

Some early studies have reported that melatonin may improve appetite, blood platelet counts, and mouth sores in people undergoing chemotherapy. But a study of melatonin's ability to ease the effects of chemotherapy on the blood counts of lung cancer patients found that high doses of the hormone had little effect. More research is needed to clarify these results.

There is relatively good evidence that melatonin supplements can influence sleep and fatigue and can help with jet lag and some sleep problems. Research has not yet shown the most effective way to use melatonin supplements for patients with sleep disorders or for people who have trouble sleeping occasionally. Some research shows that melatonin affects not only how quickly people fall asleep but also the duration and quality of sleep.

Are there any possible problems or complications?

This product is sold as a dietary supplement in the United States. Unlike drugs (which must be tested before being allowed to be sold), the companies that make supplements are not required to prove to the Food and Drug Administration that their supplements are safe or effective, as long as they don't claim the supplements can prevent, treat, or cure any specific disease.
Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Actual amounts per dose may vary between brands or even between different batches of the same brand.
Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

There appear to be few short-term side effects from taking melatonin. Some people report headaches or feeling drowsy or confused after taking it. People taking high doses have reported nightmares and trouble sleeping.

The effects of long-term use of melatonin and how it interacts with other medicines or supplements are unknown. Some reports have indicated that melatonin may interact with blood-thinning medicines and with medications for seizures or diabetes. People taking these medicines should speak with their doctors before taking melatonin.

Since melatonin may have an effect on hormone levels, women who are trying to conceive, are pregnant, or are breast-feeding should not use this supplement. The National Institute on Aging has also warned that melatonin may constrict blood vessels, which could be dangerous for people with high blood pressure or heart disease. Some practitioners believe that children and people under the age of 40 should not take melatonin because their bodies make enough of the hormone naturally. Some also caution people with severe mental illness and those taking steroid medications against using melatonin.

Because it has antioxidant properties, concerns have been raised that melatonin might interfere with radiation therapy or chemotherapy, possibly making these treatments less effective. While this concern is based largely on theories of how cancer treatments work, it is supported by some recent studies. For this reason, people being treated for cancer should speak with their doctors before taking this supplement.

Some experts also suggest that people with immune system disorders (such as severe allergies, rheumatoid arthritis, or cancers such as lymphoma) should not take melatonin because it may further stimulate the immune system and worsen these conditions. Again, this is based on a theory and not scientific evidence, but people with immune system problems should speak with their doctors before taking this supplement.

Relying on this type of treatment alone, and avoiding or delaying conventional medical care for cancer, may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer


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Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 11/01/2008
Last Revised: 11/01/2008