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Smoking cannabis ‘worse for lungs than tobacco’

Smoking cannabis is linked to more respiratory problems than smoking tobacco, according to a UK study in general practice.

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.

Even after taking into account the risk from the tobacco they smoked in joints and from also smoking cigarettes, the cannabis users still had a significantly higher rate of symptoms such as bringing up phlegm – the rate of which was increased by 0.4% with each additional joint-year of cannabis use.

Similarly, after accounting for the tobacco-related risk, each additional joint-year of cannabis use was associated with a 0.3% greater prevalence of COPD.

Dr Roy Robertson, from the University of Edinburgh, and colleagues concluded: ‘In a general practice-based sample of established adult tobacco and cannabis users, cannabis use… was associated with greater reporting of respiratory symptoms. In particular, the slightly increased presence of cough, wheeze, and sputum production are more likely in cannabis smokers.

‘In addition, it was also associated with objective evidence of COPD.’

They added: ‘Part of the adverse effect of cannabis is likely attributable to the tobacco included in the cannabis joint; however even after this additional tobacco smoked with cannabis was taken into account, the effects of cannabis on increased respiratory symptoms and increased prevalence of spirometric COPD were still apparent.’

Br J Gen Pr 2014; available online 26 January


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