The respiratory effects of cannabis dependence in young adults

Aim. To evaluate the relationship between cannabis dependence and respiratory symptoms and lung function in young adults, while controlling for the effects of tobacco smoking. Setting and participants. Nine hundred and forty-three young adults from a birth cohort of 1037 subjects born in Dunedin, New Zealand in 1972/1973 were studied at age 21. Measurements. Standardized respiratory symptom questionnaires were administered. Spirometry and methacholine challenge tests were undertaken. Cannabis dependence was determined using DSM-III-R criteria. Descriptive analyses and comparisons between cannabis-dependent, tobacco-smoking and non-smoking groups were undertaken. Adjusted odds ratios for respiratory symptoms, lung function and airway hyper-responsiveness (PC20) were measured. Findings. Ninety-one subjects (9.7%) were cannabis-dependent and 264 (28.1%) were current tobacco smokers. After controlling for tobacco use, respiratory symptoms associated with cannabis dependence included: wheezing apart from colds, exercise-induced shortness of breath, nocturnal wakening with chest tightness and early morning sputum production. These were increased by 61%, 65%, 72% (all p<0.05) and 144% (p<0.01) respectively, compared to non-tobacco smokers. The frequency of respiratory symptoms in cannabis-dependent subjects was similar to tobacco smokers of 1-10 cigarettes/day. The proportion of cannabis-dependent study members with an FEV1/FVC ratio of <80% was 36% compared to 20% for non-smokers (p = 0.04). These outcomes occurred independently of co-existing bronchial asthma. Conclusion. Significant respiratory symptoms and changes in spirometry occur in cannabis-dependent individuals at age 21 years, even although the cannabis smoking history is of relatively short duration.