Country laws, state laws, shipping regulations all seem like they could vary greatly, so I'm not sure there's a really simple answer.
Plus, I don't know for certain, but I expect you can get a doctor's prescription for it, so that could also impact things, but again, depends on where you're at and where they'd be getting shipped/purchased from.
The other important question is, if they ARE illegal for you to purchase and use without a prescription, what are the penalties? Are we talking misdemeanor, felony, or infraction/fines?