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Effects of cannabis on pulmonary structure, function and symptoms
  1. Sarah Aldington1,
  2. Mathew Williams1,
  3. Mike Nowitz2,
  4. Mark Weatherall3,
  5. Alison Pritchard1,
  6. Amanda McNaughton1,
  7. Geoffrey Robinson1,
  8. Richard Beasley1
  1. 1
    Medical Research Institute of New Zealand, Wellington, New Zealand
  2. 2
    Pacific Radiology, Wakefield Hospital, Wellington, and Wellington School of Medicine and Health Sciences, Wellington, New Zealand
  3. 3
    Wellington School of Medicine and Health Sciences, Wellington, New Zealand
  1. Professor Richard Beasley, Medical Research Institute of New Zealand, P O Box 10055, Wellington 6143, New Zealand; Richard.Beasley{at}


Background: Cannabis is the most widely used illegal drug worldwide. Long-term use of cannabis is known to cause chronic bronchitis and airflow obstruction, but the prevalence of macroscopic emphysema, the dose-response relationship and the dose equivalence of cannabis with tobacco has not been determined.

Methods: A convenience sample of adults from the Greater Wellington region was recruited into four smoking groups: cannabis only, tobacco only, combined cannabis and tobacco and non-smokers of either substance. Their respiratory status was assessed using high-resolution CT (HRCT) scanning, pulmonary function tests and a respiratory and smoking questionnaire. Associations between respiratory status and cannabis use were examined by analysis of covariance and logistic regression.

Results: 339 subjects were recruited into the four groups. A dose-response relationship was found between cannabis smoking and reduced forced expiratory volume in 1 s to forced vital capacity ratio and specific airways conductance, and increased total lung capacity. For measures of airflow obstruction, one cannabis joint had a similar effect to 2.5–5 tobacco cigarettes. Cannabis smoking was associated with decreased lung density on HRCT scans. Macroscopic emphysema was detected in 1/75 (1.3%), 15/92 (16.3%), 17/91 (18.9%) and 0/81 subjects in the cannabis only, combined cannabis and tobacco, tobacco alone and non-smoking groups, respectively.

Conclusions: Smoking cannabis was associated with a dose-related impairment of large airways function resulting in airflow obstruction and hyperinflation. In contrast, cannabis smoking was seldom associated with macroscopic emphysema. The 1:2.5–5 dose equivalence between cannabis joints and tobacco cigarettes for adverse effects on lung function is of major public health significance.

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  • Funding was provided by the New Zealand Ministry of Health, the Hawke’s Bay Medical Research Foundation and GlaxoSmithKline (UK).

  • Competing interests: None.

  • Abbreviations:
    chronic obstructive pulmonary disease
    forced expiratory volume in 1 s
    functional residual capacity
    forced vital capacity
    maximum mid-expiratory flow
    residual volume
    specific airways conductance
    slow vital capacity
    total lung capacity
    carbon monoxide transfer factor

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