What Is Melatonin?

Melatonin supplements on a table
Melatonin supplements are often recommended for sleep problems. (Image credit: Melatonin supplements photo via Shutterstock)

Melatonin is a hormone produced naturally by the pineal gland in response to darkness. Levels remain high during sleep until the pineal gland tapers off production in response to light.

Melatonin's effects on sleep, other hormones and cancer are the reason it has been studied ever since its discovery in the 1950s. In the mid-1990s, synthetic melatonin became available as a nutritional supplement.

Melatonin supplements are often recommended for sleep problems involving sleep cycles, such as jet lag or irregular night shift work.  Melatonin supplements are also recommended for sleep disorders due to side effects from beta-blockers (blood pressure medication), from stopping benzodiazepine drugs or from quitting smoking. Melatonin may also be given for insomnia linked to attention deficit-hyperactivity disorder (ADHD) and autism in children.

People who have trouble sleeping typically have low levels of melatonin, so melatonin supplements seem like a logical fix for insomnia. There is a high demand for sleep aids, especially in the U.S. The National Health Interview Survey done in 2002, and again in 2007, found 1.6 million US adults were using complementary and alternative sleep aids for insomnia. Melatonin was a top choice.

However melatonin dose more than influence sleep. Melatonin also regulates the start of menstruation, the length of ovulation cycles and menopause, according to the University of Maryland Medical Center. Melatonin supplements are purported to help bone loss and menopause symptoms.

Melatonin levels are also linked to cancer in various ways. Women with breast cancer typically have lower levels of melatonin than women who don't have it, according to the University of Maryland Medical Center. Similarly, men with prostate cancer typically have lower melatonin levels than men without prostate cancer. Some studies show shift-workers with irregular sleep schedules have an increased risk of cancer, according to the American Cancer Society. Melatonin may also have antioxidant effects and stimulate white blood cells, which attack cancer cells.

Occasionally, melatonin is used as a complementary medicine in cancer treatment for breast, brain, lung, prostate, head and neck, or gastrointestinal cancer. Melatonin is sometimes used to mitigate the side effects of chemotherapy including weight loss, nerve pain, weakness and a condition called thrombocytopenia.

A variety of other conditions are purported to benefit from melatonin supplements including Alzheimer’s disease, tinnitus, depression, chronic fatigue syndrome, fibromyalgia, migraine, irritable bowel syndrome and epilepsy.

Supplement makers now market melatonin in pill, liquid, chewable or lozenge form. Melatonin supplements are sold doses that can range from 1 to10 milligrams. Some dietary supplements contain so-called melatonin precursors, which are converted into melatonin in the body.

Does melatonin work?

Melatonin is likely effective for several sleep issues, research shows. Studies show melatonin can encourage sleep in children who suffer from insomnia related to autism, mental retardation and other central nervous system disorders, according to the National Institutes of Health. In 2001, double-blind study of 20 children with developmental disabilities showed all but two children fell asleep faster when taking melatonin compared with a placebo. However, melatonin did not change how long the children slept once they fell asleep, according to the paper published in the Journal of Child Neurology. Melatonin is also likely effective for treating an irregular sleep cycles in blind people.

Evidence is promising, but weaker, for melatonin's effectiveness in helping people with many other conditions. Melatonin may possibly be effective for cluster headaches, especially when taken in nightly doses of at least 10 milligrams, according to the National Institutes of Health. A movement disorder called tardive dyskinesia may be helped by melatonin. Additionally, melatonin may decrease sunburn when applied to the skin as a cream before sun exposure.

Melatonin may also be effective for jet lag, especially in preventing daytime sleepiness when taken to fall asleep earlier at night, and it may shorten the time it takes to fall asleep. However, a systematic review of studies on melatonin and sleep disorders found melatonin supplements shorten the time it takes people to fall asleep faster by only about 12 minutes, according to the paper published in 2005 in the Journal of General Internal Medicine.

There is some evidence that melatonin may help cancer medications fight tumors and decrease the side effects of cancer treatment. One study of cells in a test tube found melatonin reduced the growth of slowly-metastatic breast cancer cells, meaning cancer cells that slowly start to spread to other types of tissue. Melatonin also reduced the growth of non-metastatic breast cancer cells, according to the paper published in 2001 in the journal Bioelectromagnetics. 

However, the majority of evidence on melatonin and cancer has been done in relatively small studies, according to the American Cancer Society. More research needs to be done on effects of melatonin in cancer treatment or prevention.

There is a lack of evidence about whether melatonin is effective for many of the conditions it's purported to treat. Migraines and other headaches may not respond to melatonin, nor may fibromyalgia, menopausal symptoms, osteoporosis, irritable bowel syndrome or tinnitus.

Preliminary research has shown melatonin supplements may help sleep problems in older adultswho are stopping benzodiazepines. But studies have shown melatonin is less likely to be effective in changing sleep schedules for people doing shift work. Melatonin is also likely ineffective for depression, and may actually worsen depression symptoms in some people.

Are melatonin supplements safe?

Melatonin is likely safe for most people when taken for a short-term, studies show. However melatonin may cause side effects including headache, daytime sleepiness, short-lived depression symptoms, stomach cramps, dizziness and irritability.

Melatonin supplements should be avoided in pregnancy, during breastfeeding or when trying to conceive. Children or adolescents should not use melatonin supplements as melatonin may interact with other hormones and interfere with their development.

There is some evidence that melatonin acts as an antioxidant, so it may interfere with some cancer treatments, according to the American Cancer Society. Patients currently undergoing cancer treatment should speak with their doctors before taking melatonin supplements.

Melatonin may increase the strength of the immune system, which can cause problems for people with severe allergies, rheumatoid arthritis, lymphoma and other conditions linked to overactive immune systems, according to the American Cancer Society. People with immune system disorders should speak with a doctor before taking melatonin supplements as melatonin may weaken the effectiveness of immunosuppressants.

Melatonin may slow blood clotting, so taking melatonin alongside medications that also slow blood clotting can lead to excessive bruising or bleeding. Melatonin may also produce this side effect if taken with herbs that slow blood clotting such as angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, red clover and willow.

Several drugs and treatments may interact with melatonin. Birth control increases melatonin levels in the body, so taking melatonin supplements may cause high melatonin levels. Taking melatonin supplements alongside sedatives such as benzodiazepines may cause excessive sleepiness.

The drug fluvoxamine can increase the amount of melatonin absorbed by the body, therefore enhancing the effects and side effects of melatonin supplements. Similarly, melatonin will enhance herbs with sedative effects such as calamus, California poppy, catnip, hops, Jamaican dogwood, kava, St. John's wort, skullcap, valerian and yerba mansa.

Melatonin may increase blood sugar, therefore decreasing the effectiveness of diabetes medications to lower blood sugar. Melatonin may also constrict blood vessels, which could be dangerous for people with high blood pressure or heart disease.

Supplements that contain melatonin precursors, such as L-tryptophan and 5-HTP, have not been proven effective in treating insomnia, and there are safety concerns that they may be linked to debilitating condition called eosinophilia-myalgia syndrome (EMS). 

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Lauren Cox
Live Science Contributor
Lauren Cox is a contributing writer for Live Science. She writes health and technology features, covers emerging science and specializes in news of the weird. Her work has previously appeared online at ABC News, Technology Review and Popular Mechanics. Lauren loves molecules, literature, black coffee, big dogs and climbing up mountains in her spare time. She earned a bachelor of arts degree from Smith College and a master of science degree in science journalism from Boston University.