Sounds like a scare tactic, but epidemiologist and associate professor or medicine at the University of Rochester says that an ingredient often added to cocaine, levamisole, can cause a low white blood cell count or skin tissue death.

Dr. Ghinwa Dumyati reported on levamisole toxicity in the Annals of Internal Medicine, describing the effects on two cocaine abusers. They noticed a purple-colored plaque on different parts of their bodies.

So what is levamisole and how did it get in cocaine? It’s a veterinary medicine used to deworm farm animals. It is marketed under the trade name Ergamisol. Although it was once used to treat cancer in humans, the side effects were too serious. In 2000 it was outlawed for human use in the United States; Canada followed suit in 2003. However, levamisole is frequently used by drug traffickers and dealers to cut cocaine. Cutting cocaine makes an ounce much more profitable – because only some of that ounce is actually cocaine. Drug traffickers like levamisole because it adds bulk and weight, but doesn’t create “rocks” like other additives, making the drug appear pure.

The abuse of cocaine laced with levamisole can cause the skin’s outer layer to die. Even more alarming, it can cause a lowering of white blood cells – also known as leucopenia, that can lead to agranulocytosis. Agranulocytosis is a disorder in which the bone marrow fails to make enough white blood cells. The fewer white blood cells, the harder it is to fight infection. Those with agranulocytosis are highly susceptible to serious infections that can require hospitalization.

Symptoms of agranulocytosis may include fever, sore through, and chills. Any infection will rapidly progress and the patient may develop pneumonia or even life-threatening septicemia.

How likely is it that cocaine used in the United States has this powerful de-working medicine? According to the Drug Enforcement Agency (DEA), a shockingly high 69% of cocaine seized contained levamisole. Celebrity rapper DJ AM, who died of a drug overdose in 2009, had cocaine and levamisole, among other drugs, in his body according to the coroner’s toxicology reports.