Antiretrovirals that are used to boost the levels of other HIV meds are the most likely, out of all ARVs, to have dangerous interactions with common recreational drugs, as well as with erectile dysfunction (ED) medications and tranquilizers.

The boosters, Norvir (ritonavir) and Tybost (cobicistat), are both processed by liver enzymes that also metabolize numerous recreational drugs. Consequently, the recreational drugs may be metabolized more slowly and then reach dangerous levels in the body.

Norvir and Tybost are included in the combination tablets Kaletra (lopinavir/ritonavir), Stribild (elvitegravir/cobicistat/tenofovir/emtricitabine), Evotaz (atazanavir/cobicistat) and Prezcobix (darunavir/cobicistat).The researchers found that these two boosters are most likely to interact dangerously with crystal meth, MDMA (ecstasy or molly) and mephedrone (bath salts).

In addition, there is a high level of interaction between boosters and ketamine (K), ED drugs such as Viagra, and the benzodiazepine drug class (tranquilizers such as Xanax), which may lead to toxic effects, especially with K and ED drugs. GHB and boosters are a potentially dangerous, even fatal, mix.

A separate study recently found that people living with HIV who take recreational drugs commonly skip doses of ARVs when they are planning on using, because of beliefs about potential  harmful interactions.

“There is no question that systematically skipping ARVs, especially for periods of time as will occur on a drug binge and extended use, is a serious threat to HIV treatment,” says Seth Kalichman, a professor of psychology at the University of Connecticut and the head of the meds-skipping study.

Kalichman hopes that clinicians will counsel patients about seeking recreational drug treatment. Additionally, if patients are taking such drugs, physicians should consider having them switch to ARVs that reduce the risk of dangerous interactions.