Associate Professor Bob Hancox, who led the study, says “Even people who only used cannabis once per week were likely to have a cough, bring up phlegm from the chest, and get wheezy. The good news is that if they stop smoking cannabis, these symptoms usually improve, although there was evidence that cough and wheeze may persist in those who have been long-term heavy users.”
The effect of quitting cannabis use was studied in the Dunedin Multidisciplinary Health and Development Study, which continues to follow the progress of 1037 people born in Dunedin between April 1972 and March 1973. Cannabis and tobacco smoking histories were obtained at ages 18, 21, 26, 32 and 38 years. At each assessment, participants were asked how many times they had used the drug in the previous year.
Many cannabis users already had symptoms of bronchitis (cough, sputum production, and wheeze) by the age of 21 years. These symptoms persisted or got worse at ages 26, 32, and 38 years if people continued to use cannabis weekly or more. The association between cannabis use and bronchitis symptoms remained even after tobacco smoking, asthma, and other factors were taken into account.
Dr Kyle Perrin, medical director at the Asthma Foundation says “Any form of smoking is going to affect your lungs. People who smoke marijuana, even if it is only once a week, need to realise that it will adversely affect their health.”
“The findings indicate that cannabis users are likely to develop bronchitis but that this often gets better on quitting” says Associate Professor Hancox. “However, some people who had been heavy cannabis users had a persistent cough and wheeze even after they cut down or quit. This suggests that long-term heavy cannabis smoking may have lasting effects on the airways.”
The findings appear in the European Respiratory Journal and the study was supported by the Asthma Foundation.