The Alliance for Safe Online Pharmacies, known as ASOP Global, warns that buying from one of these drug sellers is a prescription for trouble.

“These days, buying prescription drugs on the Internet is easy, but finding a safe source for those medicines is not,” said ASOP Global Founder and Executive Director Libby Baney.

50% of medicines fake

She says there are between 35,000 and 50,000 active online drug sellers and that 97% do not comply with U.S. laws. Worse still, she claims that 50% of medicines sold online are fake or counterfeit.

That's a warning echoed by the Food and Drug Administration (FDA), which has found in many instances counterfeit medicine – pills passed off as being from an established pharmaceutical company – don't even have an active ingredient, or might have ingredients that are dangerous.

Consumers aren't the only victims. In April the FDA reported that a counterfeit version of Botox was found in the U.S. and much of it had been sold to doctors' office and medical clinics.

In 2012 the agency warned consumers about a counterfeit version of the widely-prescribed ADHD drug Adderall. FDA laboratory tests revealed the counterfeit version contained the wrong active ingredient. Consumers were turning to unregulated online pharmacies to buy it because the genuine version was in short supply.

It could contain anything

Since by their very nature counterfeit drugs are unregulated, they can be made anywhere by anyone – even in someone's basement. Since no agency is examining what the drugs contain, they have been found to contain everything from floor wax, mercury, concrete, chalk, boric acid, road tar and paint, to anti-freeze and other poisons.

“This means that consumers are just a click away from buying products that may cause harm, treatment failure or even death,” Baney said.

There's an added danger to doing business with an illegal online pharmacy. You are giving your credit card or other personal information to someone who is, in fact, a criminal. If they are willing to sell you a pill that might kill you, they are certainly capable of stealing and misusing your financial information.

Illegal online pharmacies are big business, however, and Baney says the largest of them generate millions in sales each month. Because they are largely anonymous and mostly located outside the jurisdiction of the United States, it makes it very hard to prosecute them.

The only way to know if a drug is counterfeit is through chemical analysis done in a laboratory. Since you probably don't have that capability, your best advice is to only order prescription drugs from your local pharmacy or other trusted sources.