Melatonin is a hormone that regulates your circadian rhythm, or the 24-hour cycle of biological processes called your "internal body clock." It helps oversee sleep patterns and other body functions.
The pineal gland in your brain makes most of the melatonin you need from the chemical serotonin.
Commercially available melatonin is obtained from the pineal glands of cattle or is made synthetically. This form of melatonin is sold as an over-the-counter (OTC) sleep aid.
Your body's natural melatonin production is triggered by darkness and stopped by light. Melatonin levels in your blood are highest at bedtime, then fall and stay very low during the day.
Much research has been done on melatonin, but there is no strong evidence that the hormone taken as a supplement can help with most sleep problems, including insomnia, in most patients. Some evidence exists for its efficacy in brain-damaged patients as a sleep aid.
Melatonin supplements also may be effective in other unique circumstances. They can help a condition called delayed sleep phase syndrome. A person with this condition has difficulty falling asleep until very late at night, but then wakes early in the morning. In 2004, the Agency for Healthcare Research and Quality (AHRQ) concluded that melatonin supplements could be effective for this condition when taken for a short time: days or weeks. AHRQ did not recommend taking them for a longer period. Melatonin may also help with significant jet lag, but studies are not clear whether it acts to alleviate daytime fatigue or to treat sleep disturbances associated with time zone changes.
Short-term side effects of melatonin supplements tend to be mild. They include nausea, headache, dizziness, fatigue, and nightmares. In addition, melatonin may interact with other OTC or prescribed drugs. More research is needed to understand the short and long-term effects of melatonin.
OTC melatonin supplements come in a variety of brands. It is important to recognize that these different brands may differ in dosage, potency, and/or ingredients.
Before taking an OTC melatonin supplement, discuss your sleep problem with your health care provider. Melatonin should not be used by people taking blood-thinning medications or by women who are pregnant, may become pregnant, or are breastfeeding. Caution should be used in people who take blood pressure medications and those with diabetes and depression disorders. Your health care provider can tell you the possible benefits and risks of taking melatonin.