Since it’s a natural hormone the body already has ways to get rid of it. It has a half-life of less than an hour. The lethal dose is so high we haven’t been able to intentionally kill animals with it: “Melatonin is not fatal even at a dose of 800 mg/kg in animal studies”.
The big risk of ongoing high doses is becoming so dependent on it that you wake up as soon as it wears off (e.g. after only 4 hours of sleep). At this level you basically can’t sleep without it and have to slowly wean yourself off to get back to normality.
The funny thing is that YouTube’s code is already so laggy that we all believed this without a second thought.