My understanding is because it is sold as a food supplement in the U.S while the UK, for example regulates it as a medicine.

So its available for prescription for short-term treatment of sleep disordersm, with provisos such as:

"Melatonin’s metabolism is mainly mediated via CYP1A enzymes. Therefore interactions may occur between melatonin and other drugs affecting or metabolised by CYP1A enzymes e.g. fluvoxamine, cimetidine, ciprofloxacin and other quinolones, carbamazepine, omeprazole, oestrogens (oral contraceptives and HRT), rifampicin, theophylline and increase in blood pressure with nifedipine and reduced prothrombin with warfarin have been reported." etc.

No need for a prescription in France.

I guess it is dangerous in regard to driving ability and misuse. You need an approval from a doctor.

Thanks for the answers. Strange that different EU countries seem to regulate differently. And then I guess I can legally order it online from Italy, France, Spain or Hungary, and get it delivered to Germany. But not buy it locally...

No need for a prescription in Italy.

You don't need prescription for melatonin in Hungary.