Low strength evidence from a systematic review and meta-analysis published in the Annals of Internal Medicine suggests that smoking marijuana may be associated with cough, sputum production, and wheezing.
Rates of marijuana use are climbing. Up to 13.3% of American adults use marijuana, and rates in young adults have doubled from 10.5% in 2002 to 21.2% in 2014. Most marijuana is consumed by smoking or vaping, which gives rise to concerns about effects on pulmonary function and respiratory health.
Mehrnaz Ghasemiesfe, MD, of the University of California, San Francisco, and San Francisco Veterans Affairs Medical Center in San Francisco, and colleagues examined the association between marijuana and respiratory symptoms, pulmonary function, and obstructive lung disease in adolescents and adults. The researchers used PubMed, Embase, PsycINFO, MEDLINE, and the Cochrane Library to identify observational and interventional studies that reported pulmonary outcomes of adolescents and adults who used marijuana.
A total of 22 studies were included in the analysis. The investigators pooled data from studies of similar design with low or moderate risk for bias and sufficient data. Results of a pooled analysis of 2 prospective studies indicated that use of marijuana was associated with an increased risk for cough (risk ratio [RR], 2.04) and sputum production (RR, 3.84), whereas pooled analysis of cross-sectional studies demonstrated an increase in cough (RR, 4.37), sputum production (RR, 3.40), wheezing (RR, 2.83), and dyspnea (RR, 1.56). The researchers noted that effects on pulmonary function and obstructive lung disease could not be determined as the data were not sufficient.
Marijuana may be expected to cause respiratory symptoms, according to the authors. Marijuana cigarettes may contain up to 20 times more particulate matter, toxic gases, reactive oxygen species, and polycyclic aromatic hydrocarbons than tobacco smoke. They did note that they found no evidence for impairment in spirometric indices in marijuana users; however, they caution that low-strength evidence suggests increased airway resistance with marijuana use, which can occur before changes in lung function.
Several study limitations included the exclusion of non-English language studies, the lack of long-term data, the inadequate assessment of exposure, the failure to report effect size or details on exposure in some studies, and heterogeneity in assessing marijuana use.
The authors argued that our current understanding of marijuana’s effects on pulmonary function is insufficient, and that given the expanding use of this drug, large-scale longitudinal studies are needed to examine long-term pulmonary effects of daily marijuana use.
Ghasemiesfe M, Ravi D, Vali M, et al. Marijuana use, respiratory symptoms, and pulmonary function: a systematic review and meta-analysis. Ann Intern Med. 2018;169(2):106-115.