Unless the law has been changed, it used to be legal to buy three months supply of a drug outside the US, as long as you had a prescription. This FDA site doesn't say it's illegal, just potentially dangerous. I believe it is illegal, but the FDA doesn't have the man-power to enforce it. From the article linked above:
"The FDA warns that it can't attest to the safety of U.S. drugs purchased outside the country, so it prohibits consumers from buying them. But the agency admits it doesn't have the resources to enforce its ban, and state and local prosecutors say they won't take action against consumers who violate the law."
http://www.biohope.org/media/article_print.cfm?articleid=2981
I just took a look at the FDA website. It's not automatically illegal to buy drugs from outside the country, but there are rules and regulations which must be followed.
http://www.fda.gov/oc/opacom/hottopics/importdrugs/default.htm It is so, so ironic that erstwhile conservatives throw their principles away when a Democrat is at stake. I've been buying drugs (glucophage for Type 2 diabetes) via mail order from an overseas supplier for years. It costs less than half what it would cost here in the US. Every package I got had a US customs stamp on it. Now, apparently the prescription drug manufacturers are losing too much money so they don't want us to buy cheap drugs from overseas anymore.
I don't know about you but I think that's ridiculous.