Melatonin
Often called the sleep hormone: made by the pineal gland, deep in the brain, from evening through the night while it is dark. It tells the body it is night; it is not a strong sleeping pill.
Melatonin is a hormone from the pineal gland, a small gland deep in the brain. Evidence: solid Your body clock has it released as evening comes, and it stays up through the night. Evidence: solid Its job is timing: it tells the body's organs and clocks that it's night. Evidence: solid Animals make it at night whether they're active by day or by night, so it marks darkness, not sleep itself. Evidence: solid
Light holds it back. In 1980, bright light at night held it back in six people; ordinary room light didn't in that study. Evidence: decent A later study of 116 young adults found that room light in the evening does: compared with dim light, melatonin started later in almost all of them, and its night-time signal was about 90 minutes shorter. Evidence: decent
Where it gets oversold: the pill. As a supplement it works mainly as a timing signal that can shift the body clock, not as a strong sleeping pill. Evidence: decent Across 19 trials of about 1,700 adults and children with sleep disorders, it got people to sleep about seven minutes faster and added about eight minutes of sleep. Evidence: decent
Why it matters
Melatonin is modest, not magic covers the pill and what to fix first. In a near-dark lab, 12 young adults reading on a tablet at full brightness for four hours, five evenings running, had their evening melatonin cut by about 55% and its rise pushed about an hour and a half later. Evidence: decent In a normal lit room a screen adds less, which is the honest version of phone out of the bedroom. Evidence: worth trying Sleeping in moves the evening melatonin rise later too, one reason to keep the same wake-up time, weekends included. Evidence: decent Melatonin is the timing side of sleep; the pressure side is sleep pressure. Evidence: solid