Melatonin is a hormone produced by the pineal gland that helps regulate sleep-wake cycles. Melatonin insufficiency can result in insomnia. It is commonly used as a dietary supplement to improve sleep in people with insomnia or jet lag, as well as to treat sleep disorders in blind individuals who lack normal light-dark cues. Melatonin has also been studied for its potential effects on other conditions, such as seasonal affective disorder and migraine headaches.