I wouldn't recommend it unless you've got a valid prescription. In the old days, they were fine with "doctors" working at the pharmacy prescribing the drug to you, but now, they are really cracking down on mail order medications, especially controlled substances. There have been people indicted for buying these things through the mail, and if you can't prove you've physically met with any doctor for the prescribed condition, they will indict you for a felony. Of course, that hinges on them actually catching you, but I wouldn't risk it!
Edit: the felony would be using the mail to transport illegally obtained controlled substances.