SAN DIEGO—For the first time, a study has found that cannabis use may be associated with a decreased risk of bladder cancer, researchers reported at the American Urological Association 2013 annual meeting.

In a study of nearly 82,000 men, bladder cancer developed in 279 over an 11-year period. Subjects who smoked marijuana, but not tobacco, had a significant 45% decreased risk of bladder cancer compared with those who did not, after adjusting for age, body mass index, and race and ethnicity, according to lead investigator Anil A. Thomas, MD, a researcher with Southern California Permanent Medical Group in Los Angeles. Men who smoked tobacco, but not marijuana, had a significant 52% increased risk, a finding that is consistent with numerous previous studies. Men who smoked both had a 28% increased risk.

Of the 82,000 men, 41% reported ever using marijuana and 57% reported tobacco use; 27% reported used both tobacco and marijuana.