Melatonin is a natural hormone that promotes sleep by regulating the sleep-wake cycle, particularly beneficial for older adults, those with jet lag, and individuals experiencing shift work disorder. Caution is advised in patients with autoimmune diseases or hepatic impairment, and melatonin may interact with certain medications, enhancing sedative effects or reducing its own effectiveness when combined with alcohol or inhibitors. The document also details various competitor products and sales data for melatonin supplements.