Friday, August 28, 2009

Cannabis Improves Respiratory Capacity

Effects of cannabis on lung function: a population-based cohort study

R.J. Hancox 1*, R. Poulton 1, M. Ely 1, D. Welch 1, D.R. Taylor 2, C.R. McLachlan 1, J.M. Greene 3, T.E. Moffitt 4, A. Caspi 4, M.R. Sears 3

1 Dunedin Multidisciplinary Health and Development Research Unit, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
2 Dept of Medical and Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
3 Firestone Institute for Respiratory Health, St. Joseph's Healthcare and Dept of Medicine, McMaster University, Hamilton, Ontario, Canada
4 Depts of Psychology & Neuroscience and Psychiatry & Behavioral Sciences, and Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina, USA; and MRC Social, Genetic, and Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK

* To whom correspondence should be addressed. E-mail:


The effects of cannabis on lung function remain unclear and may be different to tobacco. We compared the associations between use of these substances and lung function in a population-based cohort (n=1037).

Cannabis and tobacco use were reported at ages 18, 21, 26, and 32 years. Spirometry, plethysmography, and carbon monoxide transfer factor were measured at age 32. Associations between lung function and exposure to each substance were adjusted for exposure to the other substance.

Cumulative cannabis use was associated with higher forced vital capacity, total lung capacity, functional residual capacity, and residual volume. Cannabis was also associated with higher airways resistance but not with forced expiratory volume in 1 second, forced expiratory ratio, or transfer factor. These findings were similar amongst those who did not smoke tobacco. By contrast, tobacco use was associated with lower forced expiratory volume in 1 second, lower forced expiratory ratio, lower transfer factor, and higher static lung volumes, but not with airways resistance.

Cannabis appears to have different effects on lung function to those of tobacco. Cannabis use was associated with higher lung volumes suggesting hyperinflation and increased large-airways resistance, but there was little evidence for airflow obstruction or impairment of gas transfer.

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