Many people take a melatonin supplement (available as an over-the-counter dietary supplement) as an aid to help them sleep. Melatonin is a hormone that is produced naturally by the brain and assists with regulation of the sleep-wake cycle. When taken before bedtime, it is believed to signal the brain that it's time to be sleepy. Clinical research has shown that melatonin may lessen sleep problems associated with insomnia related to circadian rhythm sleep disorders. As with any over-the-counter medication or supplement, check with your health care provider before taking.