Melatonin is a hormone produced by the brain in response to darkness. It helps regulate the timing of circadian rhythms, which are the bodys internal clock that regulates the sleep-wake cycle. Melatonin is available as a dietary supplement in the United States and is used to improve sleep in conditions such as insomnia and jet lag. It is generally considered safe for short-term use, but there is limited evidence to support its long-term use for various conditions. Some potential side effects of melatonin include vivid dreams or nightmares, short-term feelings of depression, and it may worsen symptoms of depression in some individuals. Melatonin may also interact with certain medications and should be avoided by individuals with autoimmune disorders, seizure disorders, or depression. It is recommended to consult a healthcare provider before using melatonin, especially for long-term use or in combination with other medications.