Smokers consuming both marijuana and tobacco have an increased risk of copd

Smokers consuming both marijuana and tobacco have an increased risk of copd

A study in CMAJ reports the risk of respiratory symptoms and chronic obstructive pulmonary disease (COPD) increases when smoking both tobacco and marijuana. The increased risks however were not linked when smoking marijuana only.

The study differed from others since the population involved was older, and the incidence of tobacco smoking was lower in the 878 participants all from Vancouver, Canada aged 40 or over. The research was part of Burden of Obstructive Lung Disease (BOLD) Initiative that aims to find out the incidence of COPD in adults over 40 years old in the general population.

COPD is identified by diseased lungs and narrowed airways and linked to a high death rate.

Smokers were defined by the authors, as people having reportedly smoked at least 365 cigarettes in their lifetime and individuals who reported having smoked only marijuana.

The increased risk was linked with tobacco smoking. For smokers of both tobacco and marijuana the risk of developing respiratory symptoms was 2.5 higher and 3 times higher of having COPD as defined by spirometric testing.

"We were able to detect a significant synergistic effect between marijuana smoking and tobacco smoking," explains Dr. Wan Tan, University of British Columbia and St. Paul's Hospital and collaborators. "This effect suggests that smoking marijuana (at least in relatively low doses) may act as a primer, or sensitizer, in the airways to amplify the adverse effects of tobacco on respiratory health."

The limitations of the research were restricted to the available information on the potential differences in marijuana strength, on the variations in inhalation and the number of smokers who mix both substances in the same cigarette.

In an associated observation, Dr. Donald Tashkin, University of California Los Angeles (UCLA) says "the findings of Tan and colleagues add to the limited evidence of an association between marijuana use and COPD because their study focuses on an older population (aged 40 or older) that is at greater risk of COPD." Earlier studies were unsuccessful in discovering an additive effect of marijuana and tobacco on either chronic respiratory symptoms or abnormal lung functions in younger smokers. Dr. Tashkin remarks that "we can be close to concluding that marijuana smoking by itself does not lead to COPD."

However, Dr Wan Tan and colleagues write in conclusion that "Although our study had insufficient power to show an association between marijuana alone and increased risk for COPD, it remains uncertain whether marijuana by itself is harmful for the lungs. Larger studies are needed to address this critically important issue in the future."

"Marijuana and chronic obstructive lung disease: a population-based study"

Wan C. Tan, MB, Christine Lo, BSc, Aimee Jong, BSc, Li Xing, MSc, Mark J. FitzGerald, MB, William M. Vollmer, PhD, Sonia A. Buist, MD PhD, Don D. Sin, MD MPH for the Vancouver Burden of Obstructive Lung Disease (BOLD) Research Group

CMAJ • April 14, 2009; 180 (8). doi:10.1503/cmaj.081040.


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