Melatonin is a hormone, and is contraindicated for those with existing or predisposition to mental health conditions. In fact, that used to be a warning on the label in NY state. It's not something to play with.
It is if you accept the risks. Everything should be something to "play with". Never worked for me in any dosage, anyway, hopefully it works for others. Doesn't really matter in Europe since it's prescription only like anything else half useful. Living like a bunch of idiot slaves over here.
EDIT: looked it up, the latter category is also authorized through EU regulations, so likely EU-wide unless individual countries have specifically decided to ban them (which I think they still can in this case)