Melatonin is a natural hormone that helps regulate the sleep-wake cycle. In most people, the body produces enough of this hormone to make supplements unnecessary. Interestingly, bright lights can prevent the release of this sensitive hormone.

As an aid to sleep, melatonin is usually taken in a synthetic form that cause melatonin levels in the blood to rise much higher than they would naturally — as much as 20 times higher, according to the National Sleep Foundation (NSF).

Melatonin use is generally safe for short-term use, as there haven't been as many studies on its long-term use. As a result, it's not recommended for pregnant women, women who are trying to get pregnant, or anyone who has depression or an autoimmune disease. Side effects can include headache, dizziness, nausea and drowsiness, according to the Mayo Clinic.

Melatonin is useful for anyone who has trouble resetting their internal clock and has also been found helpful for kids with problems with their sleep-wake cycles, including developmental disorders autism, according to WebMD. But even then, melatonin should not be used for more than two to four weeks at a time and only under physician supervision.