Patients with chronic hepatitis C sharply increase their odds for liver fibrosis if they smoke marijuana on a daily basis, researchers at the University of California, San Francisco report. “We have shown that daily cannabis use is an independent risk factor for moderate-to-severe fibrosis, with users having nearly sevenfold higher risk compared with non-daily users,” the team concludes. Many hepatitis C patients substitute marijuana use for alcohol, especially if they were moderate-to-heavy drinkers before being diagnosed with hepatitis C, the researchers point out.

Their prospective cohort study involved 204 hepatitis C patients from clinics in San Francisco (Clin Gastroenterol Hepatol. 2008;6:69-75). Nearly a quarter of the subjects were also infected with HIV, and 14% reported daily or almost-daily cannabis use. The extent of liver fibrosis was rated on a scale of 0-6; 27.5% of the cohort showed zero fibrosis; 55.4% had mild fibrosis (a score of 1-2); and 17.2% had a moderate-to-severe case (a score of 3-6).

Compared with non-daily cannabis users, patients who indulged every day were more than three times likely to have moderate-to-severe fibrosis. When biopsy adequacy was controlled, the risk jumped to nearly sevenfold.

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Daily users were also more likely to have medically prescribed cannabis (57.1% vs. 8.79%) and were more frequently co-infected with HIV (39.3% vs. 18.2%). “The recommendation to avoid cannabis use might be especially important for HIV/hepatitis C virus co-infected persons, given that fibrosis is already enhanced in this group,” the researchers note.

A recent study of 315 hepatitis C patients in France reported similar findings (Gastroenterol. 2008;134:440-446).