Melatonin is a hormone in your body that plays a role in sleep. The production and release of melatonin in the brain is connected to time of day, increasing when it's dark and decreasing when it's light. Melatonin production declines with age. Melatonin is also available as a supplement, typically as an oral tablet or capsule. Most melatonin supplements are made in a lab. People commonly use melatonin for sleep disorders, such as insomnia and jet lag.