Smoking Cannabis Does Not Cause Cancer Of Lung or Upper Airways, Tashkin Finds; Data Suggest Possible Protective Effect —By Fred Gardner


O’Shaughnessy’s The Journal of Cannabis in Clinical Practice (Autumn 2005)

Smoking Cannabis Does Not Cause Cancer Of Lung or Upper Airways, Tashkin Finds; Data Suggest Possible Protective Effect —By Fred Gardner

«Marijuana smoking —“even heavy longterm use”— does not cause cancer of the lung, upper airways, or esophagus, Donald Tashkin, MD, reported at this year’s meeting of the International Cannabinoid Research Society. […]

Tashkin himself has long believed in a causal relationship, despite a study in which Stephen Sidney, MD, examined the files of some 64,000 Kaiser patients and found that marijuana users did not develop lung cancer at a higher rate or die earlier than non-users. […]

Tashkin decided to settle the question by conducting a large, population-based, case-controlled study. “Our major hypothesis,” he told the ICRS, “was that heavy, longterm use of marijuana will increase the risk of lung and upper-air-ways cancers.” […]

Exposure to marijuana was measured in “joint years” —average number of joints per day x years that number smoked. Thus if a person had smoked two joints a day for 15 years they’d have consumed for 30 j-yrs.

[…] A relative risk ratio of .72 means that for every 100 non-users who get lung cancer, only 72 people who smoke get lung cancer. All the odds ratios in Tashkin’s study turned out to be less than one!

Compared with subjects who had used less than one joint year, the estimated odds ratios for lung cancer were .78 for 1-10 j-yrs [according to the abstract book and .66 according to notes from the talk]; .74 for 10-30 j-yrs; .85 for 30-60 j-yrs; and 0.81 for more than 60 j-yrs.

The estimated odds ratios for oral/pharyngeal cancers were 0.92 for 1-10 j-yrs; 0.89 for 10-30 j-yrs; 0.81 for 30- 60 j-yrs; and 1.0 for more than 60 j-yrs. “Similar, though less precise results were obtained for the other cancer sites,” Tashkin reported. […]

There was time for only one question, said the moderator, and San Francisco oncologist Donald Abrams, M.D., was already at the microphone: “You don’t see any positive correlation, but in at least one category, it almost looked like there was a negative correlation, i.e., a protective effect. Could you comment on that?” (Abrams was referring to Tashkin’s lung-cancer data for marijuana- only smokers, 1-10 j-yrs.)

“Yes,” said Tashkin. “The odds ratios are less than one almost consistently, and in one category that relationship was significant […]»

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