I've suffered from insomnia for a long while now, and I despise taking Melatonin (300ug for the people asking, at least according to the label on it). It gives me unnerving dreams - not quite nightmares, but in some ways more anxiety inducing than a typical nightmare - and a lot of people report similar things. Without it I still have vivid, intense dreams but they're usually just very fun and nonsensical, a night on Melatonin makes them really terrible though.

It does help with actually physically getting me to sleep, but to be honest I can't really say it's good quality sleep. The feeling is almost 1:1 comparable to my usual bad days where I don't fall asleep until 6/7 and wake up 2 hours later, just extremely groggy and with a lot of mental fog, so I've stopped taking it altogether. This article is kinda worrying to me, can't even imagine what kinda weirdness external melatonin could be doing to a young mind if even tiny doses has such a strong effect on me, and I was a psychonaut in my younger party days.