Smoking cannabis is associated with symptoms of bronchitis. Little is known about the persistence of symptoms after stopping cannabis use. We assessed associations between changes in cannabis use and respiratory symptoms in a population-based cohort of 1037 young adults. Participants were asked about cannabis and tobacco use 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 ≥52 occasions over the previous year. Associations between frequent cannabis use and respiratory symptoms were analysed using generalised estimating equations with adjustments for tobacco smoking, asthma, sex and age. Frequent cannabis use was associated with morning cough (OR 1.97, p<0.001), sputum production (OR 2.31, p<0.001) and wheeze (OR 1.55, p<0.001). Reducing or quitting cannabis use was associated with reductions in the prevalence of cough, sputum and wheeze to levels similar to nonusers.Frequent cannabis use is associated with symptoms of bronchitis in young adults. Reducing cannabis use often leads to a resolution of these symptoms.
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