Table 1. Summary of studies on the association between chronic cannabis use and lung function.
| Author (year) | Subjects (n) | Tobacco control | Results |
|---|---|---|---|
| Cruickshank23 | 60 | No | No significant differences found between cannabis smokers and control with respect to FEV1 and FVC. |
| Tashkin et al.28 | 74 | Yes | No differences in spirometry results compared with those in matched and unmatched controls. A significant increase was noted in Raw and decrease in sGaw compared with those in both controls. Although not signficant, FVC was raised compared with that in both controls. |
| Hernandez et al.24 | 23 | No | Spirometry results of marijuana smokers were not significantly different from those of controls. There was also no significant difference in bronchial reactivity to histamine compared with controls. |
| Tilles et al.31 | 68 | Yes | Cannabis smoking with or without tobacco smoking was associated with a reduction in TLco (74% predicted±20%, P<0.05). In marijuana and marijuana plus tobacco smokers, both FEV1 and FVC were significantly increased compared with that in non-smokers. |
| Bloom et al.22,a | 990 | Yes | There was a significant increase in respiratory symptoms of phlegm and wheeze, but not cough or shortness of breath, in non-tobacco cigarette smokers whether or not they had ever smoked tobacco cigarettes. There was a significant decrease in FEV1/FVC compared with that in controls. There was no significant change in FEV1 in any non-tobacco-smoking category. |
| Tashkin et al.29 | 446 | Yes | Smokers of marijuana and/or tobacco had significantly increased rates of chronic cough, wheeze and sputum production. There was an increase in Raw and decrease in sGaw in male marijuana smokers but not in tobacco smokers. FEV1 and FVC of marijuana smokers were not significantly different from those of controls. |
| Sherrill et al.34 | 856 | Yes | Non-tobacco smoking was associated with chronic cough (OR=1.73), chronic phlegm (OR=1.53) and wheeze (OR=2.01). There was a significant reduction in FEV1 and FEV1/FVC ratios with previous non-tobacco smoking but not with current smoking. |
| Sherman et al.27 | 63 | Yes | Macrophage oxidant release, small airway integrity and alveolar gas exchange were similar in both non-smokers and marijuana smokers. There was no significant difference in lung function measurements between marijuana-only smokers and non-smokers. Marijuana and tobacco concurrent smokers showed a decrease in FEV1/FVC and TLco. |
| Tashkin et al.30 | 542 | Yes | No significant difference in AHR to metacholine was found in non-smokers and marijuana smokers without tobacco. Logistic regression showed a significant response to metacholine with marijuana smoking, however. No dose–response relationship was found between AHR and lifetime marijuana use. |
| Tashkin et al.36 | 394 | Yes | Although tobacco smoking showed an FEV1 decline in men, marijuana smoking was not associated with FEV1 decline in either gender. |
| Taylor et al.38,a | 1037 | Yes | After controlling for tobacco, cannabis users had an increase in wheezing, exercise-related shortness of breath, nocturnal wakening with chest tightness and morning sputum production (P<0.05). Cannabis users had decreased FEV1/FVC compared with non-smokers. There was no significant increase in AHR in tobacco or cannabis users. |
| Taylor et al.37,a | 1037 | Yes | After stratifying by use of cannabis, at each age increasing cannabis use was associated with a decline in FEV1/FVC. After adjustments for other co-variates, cannabis as a predictor was only marginally significant (P<0.09). |
| Moore et al.26 | 6728 | Yes | Marijuana use was significantly associated with chronic bronchitis symptoms, coughing on most days, phlegm production, wheezing and chest sounds without a cold. After adjustment for confounders, cannabis smoking was not associated with an FEV1/FVC ratio <70% (P=0.99). |
| Aldington et al.20 | 339 | Yes | Both cannabis and tobacco-smoking groups showed a reduction in FEV1/FVC. Tobacco reduced FEV1, whereas cannabis smoking had no effect on FEV1. Tobacco smoking was associated with macroscopic emphysema by CT, but not cannabis-only smoking. |
| Tan et al.35 | 878 | Yes | Marijuana-only smokers had no significant increase in risk for COPD as defined by symptoms and spirometry. However, concurrent use of tobacco and marijuana produced an increased risk for respiratory symptoms and COPD. |
| Hancox et al.32 | 1037 | Yes | After adjustment for tobacco, cannabis exposure was associated with increased FVC and TLC, but there was no significant association with FEV1 or FEV1/FVC. Cannabis was associated with increased Raw and lower sGaw. |
| Pletcher et al.33 | 5119 | Yes | Marijuana exposure was non-linearly associated with lung function, unlike tobacco (P<0.001). Lifetime marijuana exposure showed an increase in FEV1 over time at up to 7 joint-years and declining thereafter. FVC was significantly elevated even in heavy users up to 20 joint-years (P<0.001). Both FEV1 and FVC were increased at all exposure levels compared with those in controls. |
| Kempker et al.25 | 7716 | Yes | For cannabis smokers with 1–5 and 6–20 joint-years, there was no association with an FEV1/FVC<70% (OR=1.1). Those with over 20 joint-years did (OR=2.1). Use of marijuana in the past month was associated with increased FVC (0.13±0.03%, P=0.0001) for each additional day but no decrease in FEV1. |
| Macleod et al.21 | 500 | Yes | Cannabis and tobacco use together was associated with increased cough, sputum production and wheeze. After adjustment for tobacco use, age, gender and deprivation, each additional joint-year of cannabis was associated with 0.3% increase in the prevalence of FEV1/FVC<70%. |
Abbreviations: AHR, airway hyper-responsiveness; CT, computerised tomography; COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity; sGaw, specific airway conductance; Raw, airway resistance; TLco, transfer factor of the lung for carbon monoxide.