Effects of cannabis on lung function: a population-based cohort study

Abstract

The effects of cannabis on lung function remain unclear and may be different from those of tobacco. We compared the associations between use of these substances and lung function in a population-based cohort (n=1,037). Cannabis and tobacco use were reported at ages 18, 21, 26 and 32 yrs. Spirometry, plethysmography and carbon monoxide transfer factor were measured at 32 yrs. Associations between lung function and exposure to each substance were adjusted for exposure to the other substance. Cumulative cannabis use was associated with higher forced vital capacity, total lung capacity, functional residual capacity and residual volume. Cannabis was also associated with higher airway resistance but not with forced expiratory volume in 1 s, forced expiratory ratio or transfer factor. These findings were similar among those who did not smoke tobacco. In contrast, tobacco use was associated with lower forced expiratory volume in 1 s, lower forced expiratory ratio, lower transfer factor and higher static lung volumes, but not with airway resistance. Cannabis appears to have different effects on lung function from those of tobacco. Cannabis use was associated with higher lung volumes, suggesting hyperinflation and increased large-airways resistance, but there was little evidence for airflow obstruction or impairment of gas transfer.

Does Marijuana Pose Risks for Chronic Airflow Obstruction?

“…These findings are consistent with those of a few previous investigators who have shown a significant relationship between marijuana use and an increase in FVC (8,9), as well as increases in FRC, TLC, and residual volume (8). The mechanism for the increased lung volumes associated with marijuana smoking is speculative but may be a result of stretching the lung from the repeated deep inhalations associated with the usual technique of smoking marijuana, in which inhaled volumes are significantly larger and breathholding times after deep inhalations are much longer compared with the usual topography for smoking tobacco cigarettes (15).…”

“…This conclusion is generally supported by the results of longitudinal studies, although the latter are few in number (8,16).…”

“…The results of these studies have shown that marijuana use was uniformly associated with an increased prevalence of symptoms of chronic bronchitis (3-7), but the associations with spirometric findings have been less uniform, variably revealing no differences in forced expired volume in 1 s (FEV 1 ) or forced vital capacity (FVC) (3)(4)(5)(6), an actual increase in FVC and/or FEV 1 (8,9), and either a decrease or no change in the FEV 1 /FVC ratio (4,5,7,8,10) when comparisons were made between smokers of marijuana (either alone or adjusted for tobacco) and nonsmokers, as recently reviewed (11).…”

“…One study has also demonstrated associations of marijuana use with increases in functional residual capacity, total lung capacity, and residual volume (8), but others have not shown any differences in these subdivisions of lung volume (3,7). In those studies in which diffusing capacity for carbon monoxide has been measured, no differences have been noted between smokers of marijuana alone and nonsmokers (3,7,8).…”

“…A few studies have shown modest but statistically significant increases in airway resistance and reciprocal decreases in specific airway conductance (3,8,12), consistent with findings of mucosal edema, vascular congestion, and increased secretions in the central airways of habitual marijuana smokers (13). One study has also demonstrated associations of marijuana use with increases in functional residual capacity, total lung capacity, and residual volume (8), but others have not shown any differences in these subdivisions of lung volume (3,7).…”