Abstract
Background: Smoking cannabis is associated with airway inflammation and symptoms of bronchitis. Little is known about the persistence of these symptoms after people stop using cannabis. We assessed the association between changes in cannabis use and respiratory symptoms over 20 years in young adults.
Methods: Members of an unselected cohort born in Dunedin, New Zealand in 1972/73 (n = 1037) were asked about their use of cannabis and tobacco at ages 18, 21, 26, 32, and 38 years. Symptoms of morning cough, sputum production, wheeze, dyspnoea on exertion, and asthma diagnoses were ascertained at the same ages. Frequent cannabis use was defined as at least 52 occasions of use over the previous year. Associations between frequent cannabis and respiratory symptoms were analysed using generalized estimating equations with adjustments for concurrent tobacco smoking, asthma, sex, and age of assessment.
Results: Compared to infrequent or non-use, frequent cannabis use was associated with morning cough (odds ratio = 1.97, p < 0.001), sputum production (odds ratio = 2.31, p < 0.001), wheeze (odds ratio = 1.55, p < 0.001), but not dyspnoea (odds ratio = 1.23, p = 0.086). Reducing cannabis use was associated with a reduction in the prevalence of morning cough, sputum production, and wheeze (p < 0.05). After cutting down, previously frequent cannabis users had a similar prevalence of these symptoms to non-users. By age 38, however, cumulative heavy lifetime cannabis use was still associated with cough and wheeze even among those who had cut down.
Conclusions: Frequent cannabis use is associated with symptoms of bronchitis in young adults, independently of concurrent tobacco use. Quitting or reducing cannabis use leads to a reduction in these symptoms to similar levels to non-users. There was some evidence, however, that lifetime heavy use may have a persistent effect on bronchitis even after quitting.