Levamisole has increasingly been discovered in street cocaine as an adulterant. Recent reports have linked levamisole in street cocaine to agranulocytosis in cocaine users. It is well known that agranulocytosis is associated with therapeutic use of levamisole, and this may have led to the withdrawal of the drug from the US market. Levamisole was a US Food and Drug Administration-approved drug that has been used as an immunomodulator, a chemotherapy adjuvant, and anthelmintic medication. The purpose of adulterating street cocaine with levamisole is not known, but it has been speculated that it is added intentionally in order to potentiate the effects of cocaine. This may be supported by the recent report of metabolism of levamisole to aminorex in racehorses. Aminorex and related compounds, specifically 4-methylaminorex, or "ice," have high abuse potential because of their amphetamine-like pharmacological activity. This metabolism has not been reported in humans, and therefore the intended role of levamisole in street cocaine remains an enigma.