They have weird regulation in the US.
I forgot my contact lenses at home, and wanted to buy some over the counter (as you can do in most of Europe/World). To my great surprise, I was told than in the US it was impossible to buy contact lenses without a prescription -> (me banging me head against a wall). Finished my US stays with glasses.
On the other side, you can go to a supermarket and buy paracetamol that can kill you easily if you are not careful.