Melatonin is a hormone primarily produced by the pineal gland in the brain, which regulates sleep-wake cycles and circadian rhythms. It is often referred to as the "sleep hormone" because its levels rise in the evening, promoting sleepiness, and decrease in the morning. Melatonin is also available as a dietary supplement, commonly used to help manage sleep disorders and jet lag. Additionally, it has antioxidant properties and may play a role in various physiological processes.