Here is the best, most definitive article I have found so far on the subject.

Short version … it’s technically illegal, but if you’re bringing it into the country for your own use they are almost never going to stop you.

From WebMD (runs four short pages, no publication date posted)
http://www.webmd.com/healthy-aging/features/letter-and-spirit-of-drug-import-laws

The Letter (and Spirit) of Drug Import Laws
It’s illegal (nudge, nudge) to buy prescriptions drugs (wink, wink) from other countries.

By Neil Osterweil
WebMD Feature

Let’s make this very clear. It’s absolutely, unequivocally, without question illegal to reimport into the U.S. prescription drugs that have been exported to other countries, or to bring in substances that are banned under U.S. law, for any reason, except when you’ve got a prescription and the FDA or customs agents say it’s OK, or decide to look the other way.

Get it? Neither do we.

The old adage that “those who love the law and sausages should never watch either one being made” certainly applies to drug policy. But neither the FDA nor the U.S. Department of Homeland Security are necessarily to blame for the confusion.

Burdened by skyrocketing health care costs, consumers, employers, and insurers are looking for ways to save, and one of the most obvious targets is drug costs. Because Canada and most other industrialized nations impose price restrictions and limit what pharmacies can charge for drugs, the cost of a brand-name medication sold in Toronto can be as much as 55% less than what the identical drug is sold for just across Lake Ontario in Rochester, N.Y.

While the practice of reimporting drugs from Canada, Mexico, or other countries is still technically illegal (with the possible exceptions noted below), it is increasingly becoming a custom more honored in the breach than in the observance. The U.S. House of Representatives has passed three versions of bills that would allow consumers to import legal drugs for personal use. A similar measure, known as the Dorgan-Snowe Drug Importation bill, is currently before the Senate.

In the meantime, the mission of the FDA, as always, is to promote and protect the health of Americans. The mission of the U.S. Customs service is to enforce Federal laws and regulations as they pertain to imported substances such as drugs. And here’s where the law gets kind of squishy.

Current law says that if Granny decides she can get her heart medications more cheaply in Alberta than in Alabama, she could be busted for either bringing it over the border or having it delivered to her. Does that mean that dear Granny is likely to do a stretch in solitary? Hardly, experts say, because nobody wants to be seen putting the cuffs on elderly pensioners. Also, they’d have to arrest the governments of the states of Wisconsin, Minnesota, Illinois, Vermont, as well as many city governments and private employers who have turned north for lower-cost prescription drugs.

Don’t Ask, Don’t Tell

When it comes to the importation of drugs from foreign countries, the FDA acts a bit like Captain Renault in Casablanca who tells Rick that “I am shocked, shocked to find that gambling is going on in here!” as he gambles in Rick’s club.

Here’s how the FDA puts it in a consumer advisory on its web site:

“Don’t purchase from foreign web sites at this time because generally it will be illegal to import the drugs bought from these sites, the risks are greater, and there is very little the U.S. government can do if you get ripped off.”

And there’s the rub: the words “generally” and “at this time.” Under current law, stated in an FDA “guidance” paper titled “Coverage of Personal Importations,” the importation or interstate shipment of unapproved new drugs is prohibited. The definition of “unapproved” includes “foreign-made versions of U.S. approved drugs that have not received FDA approval to demonstrate they meet the federal requirements for safety and effectiveness. It is the importer’s obligation to demonstrate to the FDA that any drugs offered for importation have been approved by FDA.”

Under those rules, it appears to be illegal to import into the U.S. the cholesterol-lowering drug Lipitor purchased in Canada, even though the drug is made in Ireland for shipment to both the U.S. and Canada. To make things even more confusing, the FDA guidance cites “circumstances in which FDA may consider exercising enforcement discretion and refrain from taking legal action against illegally imported drugs.”

These extenuating circumstances include importing an unapproved drug for a serious condition for which there may be no effective treatment available in the U.S. But the drug can’t be marketed to U.S. citizens by distributors of the drug in question, the product can’t be considered to “represent an unreasonable risk,” and the patient doing the importing has to be ready to affirm in writing that the drug is for his/her own use. The patient also has to be willing to furnish contact details for a physician in the U.S., or provide “evidence that the product is for the continuation of a treatment begun in a foreign country.”

To hedge its bets, the FDA cautions that “even if all of the factors noted in the guidance are present, the drugs remain illegal and the FDA may decide that such drugs should be refused entry or seized. The guidance represents the FDA’s current thinking regarding the issues of personal importation and is intended only to provide operating guidance for FDA personnel. The guidance does not create any legally enforceable rights for the public; nor does it operate to bind the FDA or the public.”

As for the consequences, FDA associate commissioner for planning and policy William Hubbard told the Wall Street Journal in March 2003 that “any party participating in” an import plan in which a health insurer or claims processor helps arrange a purchase in Canada “does so at its own legal risk.” The article also quotes Hubbard as saying that “our highest enforcement priority would not be actions against consumers.”

“The agency doesn’t go after individuals, per se,” says Tom McGinnis, PharmD, director of pharmacy affairs for the FDA. “The agency has tended to focus its priorities on people making money from this illegal activity.”

McGinnis tells WebMD that the personal importation policy “has been in existence for a long time, probably since the ’50s, and that if you read it carefully, only deals with things that are not available in the U.S.” McGinnis says that the policy was intended to allow patients with serious, life-threatening conditions who have exhausted all available alternatives in the U.S. to try, under the guidance of their physicians, alternative therapies approved for the condition in other countries.

Anything to Declare?

U.S. Customs, for its part, warns travelers not to assume that medications approved abroad are also legal in the U.S., or that the labeled uses for which a drug is approved elsewhere hold true in the United States. The Customs service also cautions that:

Some medications available only by prescription in the U.S. may be sold over the counter in foreign countries. They could be dangerous to use without medical supervision.
Some drugs that appear to be made in the U.S. may be counterfeits.
It may be a violation of federal or state law to be in possession of some drugs without a prescription from a U.S. physician.
All imported medications must be properly declared to U.S. Customs.

The Customs service warns that “when the type of drug, the quantity, or the combination of various drugs arouse suspicions, U.S. Customs inspectors will ordinarily contact the nearest FDA or DEA [Drug Enforcement Administration] office for advice and will then make a final determination about whether to release or detain the article.”

And if all of the above makes perfect sense to you, we’d like to know what you’ve been taking — we’d like some, too.