A forthcoming review to be published in journal Annals of the American Thoracic Society reiterates that the ingestion of cannabis smoke poses nominal pulmonary risks compared to those associated with tobacco smoke. The author of the paper, Donald P. Tashkin, MD, emeritus professor of medicine and medical director of the Pulmonary Function Laboratory at the David Geffen School of Medicine at University of California, Los Angeles performed US-government sponsored studies of marijuana and lung function for over 30 years.

A preview of Dr. Tashkin’s forthcoming review appears on the American Thoracic Society news website here. It reads:

Dr. Tashkin found that regular smoking of marijuana by itself causes visible and microscopic injury to the large airways that is consistently associated with an increased likelihood of symptoms of chronic bronchitis that subside after cessation of use. He also found that the evidence does not indicate that habitual use of marijuana leads to significant abnormalities in lung function when assessed either cross-sectionally or longitudinally, except for possible increases in lung volumes and modest increases in airway resistance of unclear clinical significance. The author finds no clear link between marijuana use and the development of COPD or lower respiratory tract infections. In addition, “findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use,” Dr. Tashkin notes. “In summary, the accumulated weight of evidence implies far lower risks for pulmonary complications of even regular heavy use of marijuana compared to the grave pulmonary consequences of tobacco.”

The full paper will be available later this month.

In May, presenters at the annual meeting of the American Academy for Cancer Research reported that subjects who regularly inhale cannabis smoke possess no greater risk of lung cancer than do those who consume it occasionally or not at all — according to an analysis of six case-control studies, conducted between 1999 and 2012, involving over 5,000 subjects (2,159 cases and 2,985 controls) from around the world.

Last year, clinical data published in the Journal of the American Medical Association (JAMA) reported that subjects’ exposure to moderate levels of cannabis smoke, even over the long-term, is not associated with significant adverse effects on pulmonary function.

Vaporizers, which heat marijuana to a point where cannabinoid vapors form, but below the point of combustion, reduce subjects’ intake of potentially hazardous combustible compounds. In several clinical trials, investigators have concluded that vaporization is a “safe and effective” cannabinoid delivery mode that “does not result in exposure to combustion gases.” Researchers also report that vaporization results in higher plasma concentrations of THC compared to smoked cannabis.

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