In 2017, close to 90% of seized cocaine bricks were cut with the deworming drug. 

A pet dewormer commonly used to cut cocaine may cause brain damage, according to a team of Swiss researchers. 

Known as levamisole, the anti-parasite drug can lead to changes in the brain’s structure and also hurt cognitive performance, the University of Zurich team of scientists wrote in the October issue of Translational Psychiatry.

“We can assume from our findings that it is not just cocaine that changes the brain, but that the adulterant levamisole has an additional harmful effect,” said Professor Boris Quednow, the group’s lead researcher. “The sorts of cognitive impairment often exhibited by cocaine users may therefore be exacerbated by levamisole.”

The anti-worming drug isn’t a new addition to coke supplies; it started popping up in illicit powders more than a decade ago, the DEA reported at the time. Swiss authorities began noticing it sometime around 2008, the researchers wrote. 

It’s recently become less pervasive in drug supplies there, but in U.S. close to 90% of cocaine bricks seized in 2017 contained the dewormer. 

But researchers aren’t entirely clear on why it’s so popular as a cocaine additive, according to a university press release. It may draw out or heighten the effects of blow—but previous research has already shown a number of negative side effects, including a linkage to skin necrosis

And, animal testing shows it can impact the nervous system. In part that’s why researchers with the Psychiatric Hospital and the Institute of Forensic Medicine of the University of Zurich decided to take a closer look at the effects of levamisole, by testing drug users’ hair to figure out who had consumed the deworming agent with cocaine and who hadn’t. 

In one study, researchers compared 26 regular coke users with low levels of levamisole exposure, 49 users with high levels of exposure and 78 non-users in cognitive functioning tests. 

Both groups of coke users showed “significant impairments” in attention and memory—neither of which should come as any surprise to anyone who’s done a line or two. But the researchers also found that the group with more exposure to the dewormer showed much worse executive function—even though they weren’t doing more blow.

A second study used MRIs to look at how levamisole-laced cocaine affects the brain’s structure, finding that it thinned a region associated with executive functions. 

Given the findings, researchers suggested that the most immediate solution might be better purity testing, a harm-reduction approach to help users screen out tainted supplies. 

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