WEDNESDAY, April 15 (HealthDay News) -- Though smoking only marijuana wasn't linked to higher risk of chronic obstructive pulmonary disease (COPD), smoking tobacco or both marijuana and tobacco was associated with higher risk, according to research published in the April 14 issue of CMAJ, the journal of the Canadian Medical Association.

Wan C. Tan, of the University of British Columbia in Vancouver, Canada, and colleagues analyzed data from 878 subjects aged 40 years and older, who reported on their smoking history and underwent spirometric testing with albuterol.

Those who smoked tobacco were more likely to have COPD (odds ratio, 2.74) than non-smokers, the investigators found. In those who had smoked more than 50 marijuana cigarettes in their lifetime, the use of tobacco and marijuana was also associated with higher risk of COPD (odds ratio, 2.90). Those who had smoked at least 50 marijuana cigarettes, but not tobacco, had no significantly higher risk of COPD or respiratory symptoms.

"The consistency of some aspects of the available data allows us to more firmly conclude that smoking marijuana by itself can lead to respiratory symptoms because of injurious effects of the smoke on larger airways. Given the consistently reported absence of an association between use of marijuana and abnormal diffusing capacity or signs of macroscopic emphysema, we can be close to concluding that smoking marijuana by itself does not lead to COPD," writes Donald P. Tashkin, M.D., of the University of California in Los Angeles, in an accompanying commentary.

Several co-authors disclosed financial relationships with a number of pharmaceutical companies, and several such companies provided funding for the underlying study that produced data for this article.

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