Federal agents found that 69% of cocaine shipments they seized entering the U.S. were laced with levamisole, a drug used to deworm opossums. In humans, this drug can lead to a seriously weakened immune system called agranulocytosis. Twenty-one cases of agranulocytosis have been linked to the use of cocaine laced with levamisole, including one death. Many more cases go unreported. Canada is also finding levamisole in its seized cocaine shipments.