The drastic price increase of Mylan Pharmaceuticals’ EpiPen, which helps save people from life-threatening allergic reactions, provoked an uproar. After being forced to pay $608 for the life-saving medication — a nearly 400 percent increase in just five years — some users have turned to questionable places, like eBay, for reduced-price EpiPens.

Purchasing and selling prescription medications on eBay has been a practice for almost a decade now. It's a federal crime to resell or distribute controlled substances like opioids or psychoactive drugs; EpiPens, however, fall into the category of drugs that require a prescription but are excluded from the DEA’s Controlled Substances list.

“From a medical standpoint, purchasing prescription drugs online that purportedly were previously dispensed to another patient is a very bad idea,” Michael Carome, M.D., Director of the Health Research Group at Public Citizen, told Consumerist. “While the drugs may be cheaper, they are potentially unsafe because there is a much higher likelihood that such drugs may be tainted, counterfeited or deteriorated in some way. Patients should only fill prescriptions through a licensed pharmacy.”

What other medications should you avoid purchasing from websites like eBay?

Retin-A Topical Cream

Back in 2014, Nancy White made headlines after ordering a skin cream and receiving a potentially harmful prescription medication instead. The Tennessee-based IT engineer then filed hundreds of reports with eBay customer service about pharmaceutical drugs being sold illegally on the site, but the online consumer-to-consumer sales company has not made any significant changes.

Yasmin

Birth control medication Yasmin has been available for lower price on eBay. The prescription carries an increased risk of blood clots even compared to other birth control medications, and it also increases the risk of stroke, especially in smokers.

“Birth control is in common usage but no one should be using it without the supervision of a healthcare provider,” Gina Caliendo, director of pharmacy at the Mount Sinai Beth Israel Medical Center in New York, told ABC News.

Tegretol

The sale of potentially dangerous anti-seizure medication Tegretol was confirmed on eBay two years ago. This drug is especially dangerous — doctors carefully monitor patients on it because the medication usually takes a few weeks to be stepped up to a full dose. Additionally, blood tests should be performed periodically to rule out potential toxic effects to the liver and bone marrow. High doses of Tegretol can be fatal.

Excedrin

Beginning in January 2012, makers of Excedrin recalled the drug because of concerns that certain prescription opioid-type painkillers had accidentally been included in some pill bottles, resulting in a shortage of the over-the-counter painkiller. Some people turned to buying Excedrin on eBay for $100 a bottle and more, according to Consumer Reports. Quality control for Excedrin purchased online remains questionable.

Veterinary Prescription Products

Pricey pet prescription products, including heartworm preventive drugs for dogs and cats, have been commercially available through eBay for years. The AVMA reported that these products, which must be sold within a veterinarian-client-patient relationship (VCPR), can cause substantial adverse effects in animals.

Read more:

EpiPen Price Update: After Hillary Clinton Criticism, Mylan Lowers Cost Of Allergy Treatment Medication

What Is EpiPen And What Does It Do? Everything You Need To Know About Epinephrine Injection