See also:
Study finds no cancer-marijuana connection (Washington Post 2006)
Large Study Finds No Link between Marijuana and Lung Cancer (Scientific American 2006)
From Alternet October 2012
You’d think it would have been very big news in the spring of 2005 when Donald Tashkin, a professor of pulmonology at UCLA’s David Geffin School of Medicine, revealed at a conference that components of marijuana smoke, although they damage cells in respiratory tissue, somehow prevent them from becoming malignant. But headlines announcing “Pot Doesn’t Cause Cancer” did not ensue.
Tashkin will review his findings and discuss current research this Thursday in Santa Monica, California as part of a course for doctors accredited by the University of California San Francisco. (It is open to the public; pre-registration is $95.)
Tashkin has special credibility. He was the lead investigator on studies dating back to the 1970s that identified the compounds in marijuana smoke that are toxic. It was Tashkin who published photomicrographs showing that marijuana smoke damages cells lining the upper airways. It was the Tashkin lab reporting that benzpyrene — a component of tobacco smoke that plays a role in most lung cancers — is especially prevalent in marijuana smoke. It was Tashkin’s data documenting that marijuana smokers are more likely than non-smokers to cough, wheeze and produce sputum.