Be careful, in the country I live in (Austria) it is illegal to import prescription drugs. Customs made me pay a fine of about 60$ for trying to import Melatonin (and I didn't get the Melatonin either).
Amazing. In the US, melatonin just sits there right on the shelf where anybody who feels like can buy it for a couple bucks. No prescription, no ID, and extremely cheap.
The U.S. is somewhat idiosyncratic in classifying melatonin as not being a drug at all, but rather a dietary supplement, akin to natural/alternative-health stuff like St John's wort, fish-liver oil, or the various herbs used in traditional Chinese medicine. Therefore it doesn't even get to the prescription vs. OTC decision, since dietary supplements are basically unregulated, as long as they don't make medical claims on the label or in advertising.