Brendan Kiley in The Stranger:
These days, levamisole is mostly used by farmers to deworm cows and pigs—and, for some reason, it's also used by people in the cocaine trade. The DEA first reported seeing significant amounts of levamisole-tainted cocaine in 2005, with 331 samples testing positive. Then the numbers spiked: The DEA found 6,061 tainted samples in 2008 and 7,427 in 2009. One DEA brief from 2010 reports that between October 2007 and October 2009, the percentage of seized cocaine bricks containing levamisole jumped from 2 percent to 71 percent.
Which is not only sudden, but odd. Levamisole is not like other common cutting agents—sugar, baking powder, laxatives, etc.—in three important ways:
1. It's more expensive than other cuts.
2. It makes some customers sick.
3. It's being cut into the cocaine before it hits the United States.
This last mystery is the most puzzling. Typically, smugglers like to move the purest possible product—less volume means less chance of detection—and cut their drugs once they cross into the United States.
So what's the incentive to use a relatively expensive cut of something that makes your customers sick and increases your smuggling risk?