Melatonin can affect your natural sleep wake cycle. The natural level of melatonin in the blood is the highest at night. Some studies have shown that melatonin supplements may help to treat sleep disorders such as sleep phase delay, and alleviate insomnia and jet lag. Melatonin is usually safe for short-term use. Unlike many sleeping pills, the use of melatonin is unlikely to be dependent, and repeated use will not reduce the response (habituation) or have a hangover effect.