A UK study shows smoking cannabis is linked to more respiratory problems than smoking tobacco.

The study, published in the British Journal of General Practice, included 500 smokers, of whom 248 were long-term users of tobacco only and 252 were users of both cannabis and tobacco.

The cannabis smokers generally reported more respiratory symptoms, in particular bringing up phlegm, and suffering from wheezing or whistling, and were slightly more likely to have COPD – as indicated by an FEV1/FVC lower than 70% on spirometry.