Exposure to moderate levels of cannabis smoke — even over the long-term — is not associated with adverse effects on pulmonary function, according to clinical trial data published in the January 2012 Journal of the American Medical Assn.
Investigators at UC San Francisco analyzed the association between marijuana exposure and pulmonary function over a 20-year period in a cohort of 5,115 men and women in four US cities.
The data “confirmed the expected reductions in FEV1 (forced expiratory volume in the first second of expiration) and FVC (forced vital capacity)” in tobacco smokers. By contrast, “Marijuana use was associated with higher FEV1 and FVC at the low levels of exposure typical for most marijuana users. With up to 7 joint-years of lifetime exposure (e.g., 1 joint/d for 7 years or 1 joint/week for 49 years), we found no evidence that increasing exposure to marijuana adversely affects pulmonary function.”
They conclude, “Our findings suggest that occasional use of marijuana … may not be associated with adverse consequences on pulmonary function.”
The results are consistent with other reports finding no significant decrease in pulmonary function associated with moderate cannabis smoke exposure. A 2007 literature review conducted by researchers at the Yale University School of Medicine and published in the Archives of Internal Medicine found that cannabis smoke exposure is not associated with airflow obstruction (emphysema), as measured by airway hyperreactivity, forced expiratory volume, or other measures.
The largest case-controlled study ever to investigate the respiratory effects of marijuana smoking reported in 2006 that cannabis use was not associated with lung-related cancers, even among subjects who reported smoking more than 22,000 joints over their lifetime. “We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use,” stated its lead researcher, Dr. Donald Tashkin of California’s UCLA. “What we found instead was no association at all, and even a suggestion of some protective effect,” in that marijuana smokers had lower incidences of lung cancer than non-users.
Separate studies of cannabis smoke and pulmonary function indicate that chronic use may be associated with an increased risk of certain respiratory complications, such as cough, bronchitis and phlegm. However, alternative ingestion methods such as edibles, liquid tinctures, sprays or vaporizers virtually eliminate consumers’ exposure to such unwanted risk factors and have been determined to be ‘safe and effective’ methods of ingestion in clinical trial settings.
* “Association between marijuana exposure and pulmonary function over 20 years,” JAMA, January 2012.
March 6th, 2012 |By Paul Armentano, NORML Deputy Director
No adverse effect on pulmonary function from moderate levels of cannabis smoke