Table 2

Summary of observational studies on marijuana exposure and lung function

Author [ref.]Subjects nStudy designOutcomes measuredResults
Cruickshank [11]60Cross-sectionalFEV1, FVC, PO2, PCO2No significant differences found in FEV1 and FVC among cannabis smokers.
Tashkin [12]74Cross-sectionalRespiratory symptoms, FEV1, FVC, FEF25–75%, Raw, CV, ΔN2750–1250No differences in spirometry results. A significant increase was noted in Raw and decrease in sGaw. FVC was raised compared to both controls but not significant.
Hernandez [13]23Cross-sectionalFEV1, FVC, FEF25–75%, Raw, PD50RawSpirometry results of marijuana smokers were not significantly different to controls. No significant difference in histamine reactivity.
Tilles [14]68Cross-sectionalFEV1, FVC, PEFR, FRC, TLCOCannabis smoking±tobacco smoking was associated with a reduction in TLCO. In marijuana and marijuana+tobacco smokers, both the FEV1 and FVC were significantly increased compared to nonsmokers.
Bloom [15]990Cross-sectionalRespiratory symptoms, depth of inhalation, FEV1, FVC, VmaxSignificant increase in respiratory symptoms of phlegm and wheeze, but not cough or shortness of breath, in non-tobacco cigarette smokers regardless of tobacco smoking status. Significant decrease in FEV1/FVC compared to controls. No significant changes in FEV1 in any non-tobacco smoking category.
Tashkin [16]446Cross-sectionalRespiratory symptoms, FEV1, FVC, FEF25–75%, Raw, sGaw, DLCOSmokers of marijuana±tobacco had significantly increased rates of chronic cough, wheeze and sputum production. FEV1 and FVC of marijuana smokers not significantly different from controls.
Sherrill [17]856Observational cohortRespiratory symptoms, FEV1, FVC, Vmax50Non-tobacco smoking was associated with chronic cough, chronic phlegm and wheeze. Significant reduction in FEV1 and FEV1/FVC with previous non-tobacco smoking but not with current smoking.
Sherman [18]63Cross-sectionalMacrophage oxidant release, small airway integrity, FEV1, FVC, TLCOMacrophage oxidant release, small airway integrity, and alveolar gas exchange similar in both nonsmokers and marijuana smokers. No significant difference in lung function between marijuana only smokers and nonsmokers. Marijuana and tobacco concurrent smokers showed a decrease in FEV1, FVC and TLCO.
Tashkin [19]542Cross-sectionalAHRNo significant difference in AHR to methacholine found in nonsmokers and marijuana smokers without tobacco. However, logistic regression showed a significant response to methacholine with marijuana smoking. No dose–response relationship was found between AHR and lifetime marijuana use.
Tashkin [20]394Observational cohortFEV1Marijuana smoking was not associated with FEV1 decline.
Taylor [21]1037Observational cohortRespiratory symptoms, AHR, FEV1, FVCCannabis users had an increase in wheezing, exercise-related shortness of breath, nocturnal wakening with chest tightness and morning sputum production. Cannabis users had decreased FEV1/FVC compared to nonsmokers. No significant increase in AHR in tobacco or cannabis users.
Taylor [22]1037Observational cohortFEV1, FVCAfter stratifying by use of cannabis, at each age increasing cannabis use was associated with a decline in FEV1/FVC. After adjustments of other covariates, cannabis as a predictor was only marginally significant.
Moore [9]6728Cross-sectionalRespiratory symptoms, examination, FEV1, FVCMarijuana use was significantly associated with chronic bronchitis symptoms, coughing on most days, phlegm production, wheezing, and chest sounds without a cold. Cannabis smoking was not associated with an FEV1/FVC ratio <70%.
Aldington [23]339Cross-sectionalEmphysema by CT, FEV1, FVC, TLC, FRC, MMEF, SVC, RV, TLCO, sGaw, VABoth cannabis and tobacco smoking groups showed a reduction in the FEV1/FVC. Tobacco reduced FEV1, while cannabis smoking had no effect on FEV1. Tobacco smoking was associated with macroscopic emphysema by CT, but not cannabis-only smoking.
Tan [24]878Observational cohortRespiratory symptoms, COPD by spirometryMarijuana only smokers had no significant increase in risk of COPD as defined by symptoms and spirometry. However, tobacco and marijuana concurrent use produced an increased risk of respiratory symptoms and COPD.
Hancox [25]1037Observational cohortFEV1, FVC, TLC, RV, VA, TLCO, Raw, sGawCannabis exposure was associated with increased FVC and TLC, but no significant association with FEV1 or FEV1/FVC. Marijuana smoking associated with increased Raw and lower sGaw.
Pletcher [26]5119Observational cohortFEV1, FVCMarijuana exposure was non-linearly associated with lung function, unlike tobacco. Cannabis exposure showed an increase in FEV1 over time at up to 7 joint-years and declining thereafter. FVC was significantly elevated in users up to 20 joint-years. Both FEV1 and FVC were increased at all exposure levels.
Kempker [27]7716Cross-sectionalFEV1, FVCFor cannabis smokers with 1–5 and 6–20 joint-years, there was no association with an FEV1/FVC <70%. Those with >20 joint-years did have an association. 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 [28]500Observational cohortRespiratory symptoms, FEV1, FVCCannabis and tobacco use together was associated with increased cough, sputum production and wheeze. After adjustment for tobacco use, age, sex and deprivation, each additional joint year of cannabis was associated with 0.3% increase in prevalence of an FEV1/FVC <70%.

PO2: oxygen tension; PCO2: carbon dioxide tension; FEF25–75%: forced expiratory flow at 25–75% of FVC; Raw: airway resistance; CV: closing volume; ΔN2750–1250: percentage change in nitrogen concentration between 750 and 1250 mL of expired volume; PD50Raw: provocative dose required to achieve a 50% increase in airway resistance; PEFR: peak expiratory flow rate; FRC: functional residual capacity; TLCO: transfer factor of the lung for carbon monoxide; Vmax: oxygen uptake; sGaw: specific airway conductance; DLCO: diffusing capacity of the lung for carbon monoxide; Vmax50: flow rate at 50% of the expired FVC; AHR: airway hyperresponsiveness; CT: computed tomography; TLC: total lung capacity; MMEF: maximum mid-expiratory flow; SVC: slow vital capacity; RV: residual volume; VA: alveolar volume. Reproduced with modification from [2].