A man died from bone marrow failure after using the controversial drug levamisole - which drug dealers often add to cocaine.
The 20-year-old, of India, had been taking the medication - branded as Ergamisol - for the skin condition vitiligo.
After 17 days of using the drug, he began to show signs of a fever and had bloody diarrhoea, which antibiotics failed to treat.
He visited the hospital ten days after that, by which point doctors described him as having a 'toxic appearance' with pale, patchy skin.
Tests showed the unnamed college student's bone marrow was no longer producing blood cells to keep his body functioning.
While waiting to receive a stem cell transplant, he died because his body was unable to fight life-threatening infections, six weeks after his symptoms began.
A 20-year-old man died from bone marrow failure after using the controversial medicine Levamisole that is often mixed with cocaine by drug dealers
Doctors who treated the patient warned that levamisole - used to de-worm cattle - is commonly used by dealers to 'cut' cocaine.
It has been nicknamed as a 'flesh-eating' ingredient found in cocaine, after a flurry of people in the US saw their skin rot following use of the substance.
Levamisole was banned from human-consumption in the US in 1999, after evidence it could lower counts of white blood cells.
But it is used in the UK to treat roundworm infections and is an essential medicine, according to The World Health Organization.
In some developing countries, including India, levamisole is frequently used to treat skin conditions.
The patient, whose story was told in BMJ Case Reports, was taking a levamisole pill once a day for a form of vitiligo.
When he started experiencing fever and bloody stools, he took antibiotics for five days.
A bone marrow biopsy revealed the patient was missing vital white blood cells (pictured A). Two weeks later, there were even less (pictured B), leading to a diagnosis of failed bone marrow
But his symptoms persisted, leading him to doctors at Christian Medical College and Hospital in Vellore.
Dr John Titus George and colleagues said the man had 'depigmented patches over his lips, shins and forearms' on arrival.
Initially, doctors thought he may have an inflammatory bowel disease, but tests then revealed he had deficiencies in his blood cells.
Levamisole has become a major cutting agent in cocaine across the world, according to studies.
Between 40 to 90 percent of cocaine contains the drug, which can have adverse side effects - including agranulocytosis, an acute condition involving a severe and dangerous lowered white blood cell count.
In the UK, Liberal Democrat minister Norman Baker ordered an analysis of seized cocaine shipments in 2014 which showed that around 80 per cent contained the medicine.
And the UK has a higher rate of cocaine use than anywhere else in Europe, with 9.7 per cent of people having reported using the drug, according to The Office For National Statistics.
Studies have found Levamisole in 57 per cent of Spanish cocaine samples, 90 per cent of Danish samples, and 60 per