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An estimated 80 per cent of class A drug cocaine is routinely cut with poisonous veterinary drug Levamisole. iStock

An estimated 80 per cent of the class A drug cocaine sold across Britain is routinely cut with strong cow and horse deworming agent Levamisole, that can lead to flesh-eating diseases. Levamisole, commonly sold as Ergamisol, is used to treat parasitic worm infections.

The side effects of using the poisonous dewormer can be quite disturbing, including the rotting of skin in the extremities, like the ears, nose and fingers. The contaminated class A drug can also induce a reduced white blood cell count and skin discolouration.

The side-effects are expected to clear once the drug is out of a person's body, however they can reappear if there's a relapse. The news surfaced when a woman complaining of joint and abdominal pain, and open skin lesions was found to have taken cocaine tainted with the dewormer, according to a study in the British Medical Journal.

"We present the case of a 42-year-old woman suffering from vasculitis due to levamisole-contaminated cocaine, who persistently denied substance abuse," read an excerpt from the study. "Symptoms included ulcerating skin lesions, arthralgia and myalgia...The definitive diagnosis was made using hair testing for toxins."

The study's lead researcher Dr. Tjeerd van der Veer, said diagnosing patients can be very challenging when drug use is undisclosed. "[It is] essential for patients to be honest with their health care providers, so they can deliver the right care," said der Veer.

Meanwhile, Dr. Noah Craft, a dermatologist at the Los Angeles Biomedical Research Institute said, reported ABC News: "It's a little bit like having HIV. About 10 per cent of those patients will die from severe infections. They may be walking around like a time bomb."