The Effects of Marijuana Exposure on Expiratory Airflow. A Study of Adults who Participated in the U.S. National Health and Nutrition Examination Study

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Abstract
Given the inconclusive science on the long-term effects of marijuana exposure on lung function, the increasing tetrahydrocannabinol composition of marijuana over time, and the increasing legal accessibility of the substance, continued investigation is needed. To determine the independent association between recent and chronic marijuana smoke exposure with spirometric parameters of lung function and symptoms of respiratory health in a large cohort of U.S. adults. This is a cross-sectional study of U.S. adults who participated in the National Health and Nutrition Examination Survey cycles from 2007-2008 and 2009-2010, using the data from standardized spirometry and survey questions performed during these years. In the combined 2007-2010 cohort, 59.1% replied that they had used marijuana at least once, and 12.2% had used in the past month. For each additional day of marijuana use in the prior month, there were no changes in percent predicted FEV1 (0.002 ± 0.04%; P = 0.9), but there was an associated increase in percent predicted FVC (0.13 ± 0.03%, P = 0.0001) and decrease in the FEV1/FVC ratio (-0.1 ± 0.04%; P < 0.0001). In multivariable regressions, 1-5 and 6-20 joint-years of marijuana use were not associated with an FEV1/FVC less than 70% (odds ratio [OR] = 1.1, 95% confidence interval [CI] = 0.7-1.6, P = 0.8, and OR = 1.2, 95% CI = 0.8-1.8, P = 0.4, respectively), whereas over 20 joint-years was associated with an FEV1/FVC less than 70% (OR = 2.1; 95% CI = 1.1-3.9; P = 0.02). For each additional marijuana joint-year smoked, there was no associated change in the mean percent predicted FEV1 (0.02 ± 0.02%; P = 1.00), an increase in percent predicted FVC (0.07 ± 0.02%; P = 0.004), and a decrease in FEV1/FVC (-0.03 ± 0.01%; P = 0.02). In a large cross-section of U.S. adults, cumulative lifetime marijuana use, up to 20 joint-years, is not associated with adverse changes in spirometric measures of lung health. Although greater than 20 joint-years of cumulative marijuana exposure was associated with a twofold increased odds of a FEV1/FVC less than 70%, this was the result of an increase in FVC, rather than a disproportional decrease in FEV1 as is typically associated with obstructive lung diseases.

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