Figure 2: Risk of chronic obstructive pulmonary disease (COPD) among participants with a history of marijuana smoking, tobacco smoking or both. COPD was defined in 3 ways: by spirometric testing (ratio of forced expiratory volume in 1 second [FEV1] to forced vital capacity [FVC] of 0.70 or less), by self-report of respiratory symptoms (presence of chronic cough with phlegm and current wheezing or shortness of breath) and by self-report of a physician’s diagnosis of COPD, chronic bronchitis or emphysema. Note: ref = reference group. *Adjusted for age, sex, ethnic background, body mass index, education, asthma and other comorbidities (i.e., heart disease, hypertension, stroke, diabetes and tuberculosis) and interaction terms for concurrent smoking of marijuana and tobacco (p = 0.001 for COPD defined by spirometric testing, p = 0.283 for COPD defined by self-reported symptoms, and p < 0.001 for COPD defined by self-report of a physician’s diagnosis). †Participants who had smoked at least 365 tobacco cigarettes. ‡Participants who had smoked at least 50 marijuana cigarettes.