Melatonin is a hormone naturally produced in the human body by the pineal glands, and one that regulates the sleep cycle. The level of melatonin in your body is always changing. It tends to be higher in the mid-evening, at its highest levels at night, and then it gradually decreases by early morning. Young adults produce more melatonin, and very old adults sometimes have none. In winter when there is less daylight, the human body sometimes produces melatonin too early or too late in the day, leading to seasonal affect disorder or winter depression. Melatonin is found naturally in some meats, fruits, vegetables and grains. A manmade version is marketed as a dietary supplement to help people suffering from insomnia. This herbal remedy is also used to treat chronic cluster headaches, seasonal affect disorder, and confusion after surgical procedures. People who work night shifts sometimes use melatonin to adjust their sleep cycles. Some studies indicate that melatonin can have a positive effect on the immune system and even slow down cancer as well as the aging process, but more research needs to be done. Side effects of taking melatonin can be morning grogginess, sleepiness, unusually vivid dreams, and alterations in blood pressure. Like with most sleep aids, melatonin can be habit forming.