Smoking marijuana may increase risk of lung problems

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Smoking marijuana once a week can cause coughing, wheezing and phlegm – all signs of chronic bronchitis, an evidence review by researchers at University of California-San Francisco, San Francisco Veterans Affairs Medical Centre, San Francisco, The Wright Centere for Graduate Medical Education, Scranton, Pennsylvania, Memorial Sloan Kettering Cancer Centre, New York, and the University of Toronto, reports.

Marijuana smoking doubles a person's risk of developing a regular hacking cough. It also triples the risk of coughing up phlegm and suffering from wheezy constricted breathing, Health24 reports researchers found.

"We know that smoke from tobacco and other entities – including burning wood in your fireplace – causes chronic bronchitis, so it's not at all surprising they found chronic bronchitis in prior marijuana research," said Dr Norman Edelman, senior scientific adviser to the American Lung Association.

Edelman said he's concerned that heavy marijuana use could lead to larger health problems for those who develop chronic bronchitis. "You would worry about people being more susceptible to pneumonia, and of course, the end result of chronic bronchitis, if it persists long enough and is severe enough, is what we call COPD – chronic obstructive pulmonary disease," Edelman said. About half of tobacco smokers get COPD, he said. "It will be interesting to see what percentage of regular marijuana smokers get COPD," he added.

Paul Armentano, deputy director of NORML, a group supporting reform of marijuana laws, said the study findings are "consistent with prior data". "It is hardly surprising that the habitual inhalation of combustive smoke may be associated with specific, though generally mild respiratory symptoms, like cough," he said.

"However, unlike the inhalation of tobacco smoke, cannabis smoke exposure – even long-term – is not associated with the kind of serious respiratory effects that are often identified with long-term tobacco use, such as COPD, emphysema or lung cancer," Armentano said.

About 13% of adults and 21% of young adults are believed to be regular marijuana users. Marijuana legalisation has led to the development of many alternatives to smoking dagga, such as cannabis-infused edibles, oils and concentrates, Armentano said.

For the evidence review, researchers led by Dr Mehrnaz Ghasemiesfe, at the San Francisco VA Medical Centre, analysed data from 22 studies of the effects of marijuana smoking on lung health.

Analysis of two prospective studies (ones that watch for outcomes such as disease development) found dagga smoking associated with a doubled risk of cough and a nearly quadrupled risk of phlegm, the results showed.

Combined analysis of other studies revealed an increased risk of cough (4.3 times); phlegm (3.4 times); wheezing (2.8 times); and shortness of breath (1.5 times). Some are concerned that as more US states legalise dagga, more people will develop lung problems.

"Because some of the worst effects of smoking take years to show effect, it took time until we had established clear and undeniable risks of cancer, heart disease and other major medical problems that were caused by smoking tobacco," said Dr Adam Lackey, chief of thoracic surgery at Staten Island University Hospital.

"I worry that we are looking at a similar situation with marijuana," he said. "People need to realise that we just don't know yet what the long-term effect of marijuana smoking is. This study shows that marijuana smoking certainly isn't totally benign."

At the same time, Edelman doubts marijuana will be as harmful as tobacco, simply because it's not smoked as much. "My guess is that not many marijuana users smoke 20 joints a day, which would be equivalent to a pack a day for a cigarette smoker," he said.

"I don't think the smoke of marijuana is necessarily less toxic than the smoke of tobacco. It's just that in general, people who use marijuana smoke fewer marijuana cigarettes than people who smoke tobacco," Edelman said.

Abstract
Background: The health effects of smoking marijuana are not well-understood.
Purpose: To examine the association between marijuana use and respiratory symptoms, pulmonary function, and obstructive lung disease among adolescents and adults.
Data Sources: PubMed, Embase, PsycINFO, MEDLINE, and the Cochrane Library from 1 January 1973 to 30 April 2018.
Study Selection: Observational and interventional studies published in English that reported pulmonary outcomes of adolescents and adults who used marijuana.
Data Extraction: Four reviewers independently extracted study characteristics and assessed risk of bias. Three reviewers assessed strength of evidence. Studies of similar design with low or moderate risk of bias and sufficient data were pooled.
Data Synthesis: Twenty-two studies were included. A pooled analysis of 2 prospective studies showed that marijuana use was associated with an increased risk for cough (risk ratio [RR], 2.04 [95% CI, 1.02 to 4.06]) and sputum production (RR, 3.84 [CI, 1.62 to 9.07]). Pooled analysis of cross-sectional studies (1 low and 3 moderate risk of bias) showed that marijuana use was associated with cough (RR, 4.37 [CI, 1.71 to 11.19]), sputum production (RR, 3.40 [CI, 1.99 to 5.79]), wheezing (RR, 2.83 [CI, 1.89 to 4.23]), and dyspnea (RR, 1.56 [CI, 1.33 to 1.83]). Data on pulmonary function and obstructive lung disease were insufficient.
Limitation: Few studies were at low risk of bias, marijuana exposure was limited in the population studied, cohorts were young overall, assessment of marijuana exposure was not uniform, and study designs varied.
Conclusion: Low-strength evidence suggests that smoking marijuana is associated with cough, sputum production, and wheezing. Evidence on the association between marijuana use and obstructive lung disease and pulmonary function is insufficient.

Authors
Mehrnaz Ghasemiesfe, Divya Ravi, Marzieh Vali, Deborah Korenstein, Mehrdad Arjomandi, James Frank, Peter C Austin, Salomeh Keyhani

Health24 report Annals of Internal Medicine abstract

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