Marijuana Smoking Associated With Rapid Decline in FEV₁ for Older Adults

This article is part of Pulmonology Advisor‘s coverage of the American Thoracic Society’s International Conference, taking place in San Diego, California. Our staff will report on medical research related to asthma and other respiratory conditions, conducted by experts in the field. Check back regularly for more news from ATS 2018.

SAN DIEGO — Marijuana smoking leads to rapid decline in forced expiratory volume (FEV₁) in adults ≥ 40 years, imparting risks similar to cigarette smoking, according to research presented at the annual American Thoracic Society International Conference, held May 18-23, 2018, in San Diego, California.

“We hypothesized that the effects of marijuana smoking on lung function are determined by the lifetime burden of smoking,” stated lead author Wan-Cheng Tan, MD, associate professor at the The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, British Columbia University in Vancouver.

This study’s principal aim was to determine the longitudinal effect of marijuana smoking on the FEV₁ of adults ≥ 40 years. Researchers recruited 5291 participants from the general population in Canada. Participants were interviewed via questionnaires to determine respiratory history and marijuana and tobacco smoking. The study subgroups included 43.5% (n=2299) who never smoked marijuana or tobacco, 36.4% (n=1926) who only smoked cigarettes, 3.4% (n=181) who only smoked marijuana, and 16.7% (n=885) who smoked both marijuana and cigarettes. To determine whether smoking marijuana was associated with increased decline in FEV₁ compared with the non-marijuana and non-cigarette smokers, study investigators used a linear mixed effects model. 

To establish a baseline, spirometric tests were performed on a longitudinal cohort of individuals before and after they received 200 µg of salbutamol. Thereafter, participants were assessed at 18-month intervals. Adjustments were made for baseline FEV₁, concomitant tobacco smoking, sex, age, body mass index, and the interface between time and FEV₁ at baseline.

The increased FEV₁ decline for marijuana smokers vs nonsmokers (β -14.57; 95% CI, -22.74 to -6.41) was similar to that of cigarette smokers vs nonsmokers (β -15.84; 95% CI, -21.16 to -10.52). The results demonstrate that smoking marijuana, either alone or with cigarettes, increases lung function decline, and should be regarded as a risk factor for the progression of chronic obstructive pulmonary disease.