Levamisole

Levamisole is a drug that was used to treat infections with parasitic worms, and for some forms of chemotherapy, to treat cancer. The drug was discovered in 1966. It was withdrawn from the US and Canadian markets in 2000 and 2003, because of a serious risk of side effects; better drugs can replace it. 
Currently, levamisole remains in veterinary use as a dewormer for livestock. The drugs has also been used as an adulterant in cocaine sold in the US and Canada. This use resulted in serious side effects.