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People who smoke cannabis as little as once a week are more likely to suffer respiratory symptoms such as morning cough, bringing up phlegm, and wheezing, according to University of Otago research.

However, the researchers’ study into the long-term respiratory effects of smoking cannabis found that after reducing or quitting cannabis smoking, these symptoms reduced to levels similar to those found in non-users. In New Zealand, cannabis use is almost as widespread as tobacco with about half of young adults admitting to have used it in the previous year. 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.


Serious respiratory illnesses continue to make a substantial contribution to New Zealand’s health burden. It is estimated that over 700,000 New Zealanders take medication for a respiratory condition and that respiratory diseases account for 1 in 8 of all hospitalisations in New Zealand – over 69,000 admissions including 23,000 admissions for children. Respiratory disease was the cause of over 2,700 deaths in 2011 and costs New Zealand over $5.5 billion every year.


  • Over 500,000 New Zealanders have asthma
  • One in seven children (107,000) and one in nine adults (389,000) have asthma
  • In 2013 asthma was responsible for 7,400 hospitalisations
  • People still die from asthma, with 69 deaths in 2011
  • In the five years between 2006 and 2011:
    • Asthma deaths were six times higher for Pacific Peoples and five times higher for Maori compared to NZ European
    • People in the most deprived areas were three times more likely to die of asthma than people in the least deprived areas
    • Children living in the most deprived areas were more likely to have asthma (15%) than children living in the least deprived areas (10%)
  • Maori have a higher prevalence of asthma compared to non-Maori children, tend to have more severe symptoms, require hospitalisation for asthma almost three times as often, and require more time off school because of asthma
  • $800,000,000 is the conservative estimate of the annual economic burden of asthma
  • Asthma affects approximately 235 million people worldwide and the prevalence is rising
  • Asthma causes an estimated 250,000 deaths worldwide annually
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