Melatonin is both a hormone and a very powerful antioxidant. It's truly amazing, but our brains are supposed to make melatonin to help us to use our internal clocks so that we get sleepy regularly at the right time and want to go to bed. Obviously, as in all things dealing with bodies, individuals vary greatly.
https://www.hopkinsmedicine.org/health/wellness-and-prevention/melatonin-for-sleep-does-it-work