Melatonin is a naturally occurring hormone that is produced by the pineal gland in the brain. It plays a crucial role in regulating the sleep-wake cycle, also known as the circadian rhythm. Natural levels of melatonin in the blood are highest at night. Some research suggests that melatonin supplements might help treat sleep disorders, such as delayed sleep phase. People commonly use melatonin for insomnia and improving sleep in different conditions, such as insomnia and jet lag. It is also used for depression, chronic pain, dementia, and many other conditions.  

Melatonin helps regulate your body temperature, blood pressure, blood glucose, body weight, and levels of some hormones. Melatonin also binds to receptors in your body to help you relax. For instance, it binds to receptors in your brain to reduce nerve activity. It can also reduce levels of dopamine, a hormone that helps you stay awake, and is involved in some aspects of the day-night cycle of your eyes. The most common melatonin side effects include headache, dizziness, nausea, and daytime drowsiness.