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If you buy cocaine in the UK there's an 80 per cent chance that it's been cut with veterinary dewormer that causes human flesh to rot.
Powerful cow and horse deworming agent levamisole is now routinely used to cut the class A drug - and the side effects are horrific.
A new study in the British Medical Journal says doctors were trying to treat a woman with open skin lesions and severe abdominal and joint pain but were stumped as to the cause of her symptoms.
After running chemical tests on her hair, the team realised that the condition was caused by levamisole-tainted cocaine she'd taken.
Levamisole poisoning can cause skin lesions and discolouration and rotting of the skin when blood cells rupture, particularly in extremities such as the ears, nose and fingers.
Ingesting the chemical can also lead to a drop in white blood cell count, which leaves sufferers vulnerable to other conditions.
"It’s a little bit like having HIV," Dr Noah Craft, a dermatologist at the Harbor-UCLA Medical Center, told ABC during a 2011 spate of levamisole poisoning cases in the US.
About 10 percent of those patients will die from severe infections. They may be walking around like a time bomb.
The authors of the study said in part they wrote the report to highlight how difficult it can be to diagnose people who don't admit to drug use.
It is "essential for patients to be honest with their health care providers, so they can deliver the right care," lead researcher Dr Tjeerd van der Veer said.