Melatonin, also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes. In animals, circulating levels of the hormone melatonin vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions. Melatonin has been studied as a potential treatment of gastroesophageal reflux disease, cancer, immune disorders, cardiovascular diseases, depression, seasonal affective disorder (SAD), circadian rhythm sleep disorders, sexual dysfunction and insomnia in the elderly. Prolonged release melatonin has shown good results in treating insomnia in older adults (2007). It may ameliorate circadian misalignment and SAD. Basic research indicates that melatonin may play a role in modulating the effects of drugs of abuse such as cocaine. Melatonin is also a geroprotector.