Melatonin is a naturally occurring hormone found in most animals, including humans, and some other living organisms, including algae. Circulating levels vary in a daily cycle, and melatonin is important in the regulation of the circadian rhythms of several biological functions. Many biological effects of melatonin are produced through activation of melatonin receptors, while others are due to its role as a pervasive and powerful antioxidant with a particular role in the protection of nuclear and mitochondrial DNA. The use of melatonin as a drug can entrain (synchronize) the circadian clock to environmental cycles and can have beneficial effects for treatment of certain insomnias. Its therapeutic potential may be limited by its short biological half-life, poor bioavailability, and the fact that it has numerous non-specific actions In recent studies though, prolonged release melatonin has shown good results in treating insomnia.
Products containing melatonin have been available as a dietary supplement in the United States since 1993, and met with good consumer acceptance and enthusiasm. However, over-the-counter sales remain illegal in many other countries including some members of the European Union and New Zealand, and the U.S. Postal Service lists melatonin among items prohibited by Germany. Production of melatonin by the pineal gland is under the influence of the suprachiasmatic nucleus (SCN) of the hypothalamus, which receives information from the retina about the daily pattern of light and darkness. Both SCN rhythmicity and melatonin production are affected by non-image-forming light information traveling through the recently-identified retinohypothalamic tract (RHT).
Melatonin is a hormone produced in the brain by the pineal gland from the amino acid tryptophan. The synthesis and release of melatonin are stimulated by darkness and suppressed by light, suggesting the involvement of melatonin in circadian rhythm and regulation of diverse body functions. Levels of melatonin in the blood are highest prior to bedtime. Synthetic melatonin supplements have been used for a variety of medical conditions, most notably for disorders related to sleep. Melatonin possesses antioxidant activity, and many of its proposed therapeutic or preventive uses are based on this property. New drugs that block the effects of melatonin are in development, such as BMS-214778 or luzindole, and may have uses in various disorders.