Marijuana Use, Respiratory Symptoms, and Pulmonary Function: A Systematic Review and Meta-analysis

Abstract

Background: The health effects of smoking marijuana are not well-understood.

Purpose: To examine the association between marijuana use and respiratory symptoms, pulmonary function, and obstructive lung disease among adolescents and adults.

Data sources: PubMed, Embase, PsycINFO, MEDLINE, and the Cochrane Library from 1 January 1973 to 30 April 2018.

Study selection: Observational and interventional studies published in English that reported pulmonary outcomes of adolescents and adults who used marijuana.

Data extraction: Four reviewers independently extracted study characteristics and assessed risk of bias. Three reviewers assessed strength of evidence. Studies of similar design with low or moderate risk of bias and sufficient data were pooled.

Data synthesis: Twenty-two studies were included. A pooled analysis of 2 prospective studies showed that marijuana use was associated with an increased risk for cough (risk ratio [RR], 2.04 [95% CI, 1.02 to 4.06]) and sputum production (RR, 3.84 [CI, 1.62 to 9.07]). Pooled analysis of cross-sectional studies (1 low and 3 moderate risk of bias) showed that marijuana use was associated with cough (RR, 4.37 [CI, 1.71 to 11.19]), sputum production (RR, 3.40 [CI, 1.99 to 5.79]), wheezing (RR, 2.83 [CI, 1.89 to 4.23]), and dyspnea (RR, 1.56 [CI, 1.33 to 1.83]). Data on pulmonary function and obstructive lung disease were insufficient.

Limitation: Few studies were at low risk of bias, marijuana exposure was limited in the population studied, cohorts were young overall, assessment of marijuana exposure was not uniform, and study designs varied.

Conclusion: Low-strength evidence suggests that smoking marijuana is associated with cough, sputum production, and wheezing. Evidence on the association between marijuana use and obstructive lung disease and pulmonary function is insufficient.

Primary funding source: None. (PROSPERO: CRD42017059224).

Figure 1.. Evidence search and selection.

Some studies were assigned >1 outcome label and are counted twice. ROB = risk of bias.

Figure 2.. Association between marijuana use and cough and sputum production in prospective cohort studies.

We used the Paule–Mandel method for estimating τ². The squares indicate RRs from primary studies, and size reflects the statistical weight of the studies. The horizontal lines indicate 95% CIs. The diamonds represent the subtotal and overall RR and 95% CI. The vertical solid line shows the line of no effect (RR = 1). The pooled RR was not significant after the Knapp–Hartung small-sample adjustment for cough (P = 0.10) and sputum production (P = 0.20). RR = risk ratio.

Figure 3.. Association between marijuana use and cough, sputum production, wheezing, dyspnea, and chronic bronchitis in cross-sectional studies.

We used the Paule–Mandel method for estimating τ². The squares indicate RRs from primary studies, and size reflects the statistical weight of the studies. The horizontal lines indicate 95% CIs. The diamonds represent the subtotal and overall RR and 95% CI. The vertical solid line shows the line of no effect (RR = 1). After the Knapp–Hartung small-sample adjustment, pooled RRs were significant for cough (P = 0.05), sputum production (P = 0.05), wheezing (P = 0.01), and dyspnea (P < 0.01) but not for chronic bronchitis (P = 0.31). RR = risk ratio.