Melatonin is a hormone produced naturally by the pineal gland, a small gland in the brain, in response to darkness. It plays a central role in regulating the body’s circadian rhythm — the internal 24-hour biological clock that governs the sleep-wake cycle. Often referred to as the “sleep hormone,” melatonin signals to the body that it is time to prepare for sleep, promoting drowsiness and lowering core body temperature. Melatonin production follows a predictable daily pattern. Levels begin to rise in the evening as natural light fades, peak during the middle of the night, and then gradually decline toward morning. Exposure to bright or blue light in the evening — such as from smartphones, tablets, and computer screens — can suppress melatonin production, delaying the onset of sleepiness and potentially disrupting sleep. Melatonin supplements are widely available and are commonly used to address a variety of sleep-related issues. They are most effective for circadian rhythm disorders — conditions in which the timing of sleep is misaligned with the desired or required schedule. These include jet lag, shift work sleep disorder, delayed sleep phase disorder, and sleep disturbances in blind individuals. Melatonin is generally less effective for treating insomnia caused by anxiety or poor sleep habits, where cognitive behavioral therapy (CBT-I) is more appropriate. Melatonin supplements are available in various doses, typically ranging from 0.5 to 10 milligrams. Research suggests that lower doses (0.5 to 2 milligrams) taken 30 to 60 minutes before the desired bedtime may be as effective as higher doses with fewer side effects. Melatonin is considered generally safe for short-term use, but long-term effects and optimal dosing remain subjects of ongoing research.