You can see the signs before you even cross the border from the US into Mexico - farmacias pitching prescription drugs for a fraction of the price you'd have to pay from where you're standing. Travel further south into any given Mexican tourist town and it's hard to turn a corner without encountering farmacia signs touting cut-rate prices on everything from Viagra to Valium.

So if it's cheap, easy, and allowable, why not pick up an extra bottle of medicine that may someday come in handy? In many cases, such bargains can indeed be worthwhile, and if you're one of the many uninsured Americans, hundreds of dollars may be saved.

Furthermore, as long as the drug isn't a controlled substance, such as a narcotic, US Customs allows you to bring back as much as a three-month supply of a medication without a prescription. Even if it is a controlled substance that you want, Customs will let you bring in up to 50 dosage units without a prescription.

But that doesn't mean it's with their blessing. In fact, most public health experts in the US are united in their warnings of caveat emptor: "When it comes to going outside of the United States to buy prescription drugs, the message we really want to get to consumers is 'buyer beware,'" stresses a spokesman for the US Food and Drug Administration.

Leading the list of concerns are questions about the quality of drugs sold outside of the US. While the entire drug manufacturing process - from how and where drugs are made to how they're shipped and stored at pharmacies - is strictly controlled in the US by the Food and Drug Administration, the FDA has no jurisdiction in other countries and therefore such safety factors are often unknown.

Those allergy tablets, for instance, may look perfectly safe inside their stamped and sealed packaging, but if they've been left in extreme temperatures, their effectiveness or purity could be compromised. And then there's the chance that they might be not what the doctor ordered at all.

"There have been a number of reports of counterfeit drugs coming out of Mexico," says Marvin Shepherd, director of the Center for Pharmacoeconomics at the University of Texas in Austin. Shepherd has conducted extensive research on prescription drug importation from Mexico and says counterfeit Viagra and Prozac have been reported. He adds that there are newer concerns that counterfeit Oxycontin, a narcotic painkiller, may also be in circulation.

Mishandled or counterfeit drugs could pose such problems as having too little or too much of an active ingredient, or worse - they could be contaminated and present the risk of permanent damage the body, paralysis, organ malfunction, or even death, warns the American Pharmacists Association (APhA.)

The FDA, of course, doesn't have jurisdiction in Canada either, but the similarity of Canada's regulatory system to that of the US gives officials more confidence in drugs from that country. (That's also why prescription drugs from Canada, though cheaper than in the US, still cost more than those from countries such as Mexico.)

"If you have a less rigorous regulatory system, you're more likely to have problems with the quality of products you're working with," says Susan Winckler, vice president for policy and communications for APhA.

To avoid potential problems, experts urge travelers to use the same discretion in drug purchases as they would with any other consumer concerns in a foreign country. But when it comes to what's seen as a great bargain, to many find themselves tossing caution into the wind.

"You hear stories about people who travel to Mexico to get medications, and while they don't seem to worry about the safety of the drugs, they'll carry bottled water along with them because they don't even feel the water is safe enough to drink," says Winckler. "You have to wonder about the logic in that."

Important Tips

Despite the concerns, many people do save money on prescriptions purchased outside of the country and are satisfied with their medications. For those undeterred by the risks, here are a few important tips from the US Customs Agency and the FDA for buying prescription drugs and bringing them into the United States.

• Check the expiration date, or fecha de caducidad on any medications you purchase and make sure the amount and type of medication matches that which is described on the package.

• Directions for the proper use of drugs bought in Mexico are quite often in Spanish, or another foreign language that users may not understand. Make sure you clearly understand the directions before taking any medications.

Prescription drug use is strongly advised only in conjunction with medical supervision and follow-up. (That's the simple reason why prescriptions are required.)

• There is particular concern about the improper use of antibiotics due to the potential to easily build up resistances to such drugs. Overuse of antibiotics can lower one's ability to fight other illnesses and could even make it difficult for doctors to diagnose some potentially serious conditions.

• Remember that drugs brought into the US must be approved for use in this country by the FDA and the drugs must be in their original packaging.

• Important - When bringing medications into the US, you must declare the drugs, regardless of the amount you purchased. If you forget or are not truthful, and officials find out, the consequences could range from the drugs being taken away to your being placed under arrest.

• Even if you make it through Customs, keep in mind that state laws might still make it illegal to be in possession of certain drugs without a prescription, particularly if the drug is a controlled substance.

(Source: US Customs Agency; US Food and Drug Administration)