A 2008 study evaluated people with chronic hep C (HCV)—including some coinfected with HIV—who inhaled marijuana daily. They were found to be nearly seven times more likely to have moderate to severe liver fibrosis—scarring that can progress to cirrhosis and liver failure—than less frequent users. Adding alcohol increased the danger.

Many HIV-positive people use marijuana to increase appetite and ease nausea or neuropathy, and studies have confirmed these benefits. To maintain them while reducing the danger, try moderation: The study’s authors suggest that “HCV-infected people should be counseled to reduce or abstain from cannabis use.”