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SMOKING |
1 Medical Research Institute of New Zealand, Wellington, New Zealand
2 Pacific Radiology, Wakefield Hospital, Wellington, and Wellington School of Medicine and Health Sciences, Wellington, New Zealand
3 Wellington School of Medicine and Health Sciences, Wellington, New Zealand
Correspondence to:
Professor Richard Beasley, Medical Research Institute of New Zealand, P O Box 10055, Wellington 6143, New Zealand; Richard.Beasley{at}mrinz.ac.nz
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.
Abbreviations: COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; FRC, functional residual capacity; FVC, forced vital capacity; MMEF, maximum mid-expiratory flow; RV, residual volume; sGaw, specific airways conductance; SVC, slow vital capacity; THC, tetrahydrocannabinol; TLC, total lung capacity; TLCO, carbon monoxide transfer factor
Relevant Article
Thorax 2007 62: 1036-1037.
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  A. Agrawal, M. L. Pergadia, S. F. Saccone, M. T. Lynskey, J. C. Wang, N. G. Martin, D. Statham, A. Henders, M. Campbell, R. Garcia, et al. An Autosomal Linkage Scan for Cannabis Use Disorders in the Nicotine Addiction Genetics Project Arch Gen Psychiatry, June 1, 2008; 65(6): 713 - 721. [Abstract] [Full Text] [PDF]
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 P. Lange Cannabis and the lung Thorax, December 1, 2007; 62(12): 1036 - 1037. [Full Text] [PDF]
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