melatonin
n. B2 Upper Intermediate US //ˌmɛɫəˈtoʊnɪn// UK //mˈɛlɐtˌɒnɪn// mela·tonin
n. a natural chemical in your body that helps you fall asleep. It is often found in supplements to help people with sleep problems.
n. a hormone secreted by the pineal gland that regulates the sleep-wake cycle. It is also available as a pharmaceutical supplement to treat insomnia and jet lag.
I take a melatonin tablet an hour before bed to help me sleep.
Many people use melatonin supplements when traveling across time zones to adjust their internal clocks more quickly.
While melatonin is effective for short-term sleep regulation, long-term reliance on synthetic supplements may disrupt the body's natural circadian rhythms if not managed carefully.
From mela- + tone + -in, ultimately from Ancient Greek μέλας (mélas, “black, dark”).