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Occasional Marijuana Use Does Not Harm Lung Function

Marijuana (cannabis) leaf

The following study results about marijuana use will be applauded by some and booed by others, but here goes: a University of California, San Francisco, research team found that occasional marijuana use does not harm lung function, but that heavy use is associated with an increased decline in pulmonary function. The new study appears in the January 11 issue of the Journal of the American Medical Association.

Medical marijuana use has positive effects

The research team, under direction of Mark J. Pletcher, MD, MPH, noted that use of marijuana has “beneficial effects on pain control, appetite, mood, and management of other chronic symptoms,” and suggested that “occasional use of marijuana for these or other purposes” may not result in harm to lung function.

The debate over the safety of medical marijuana has been a vigorous and contentious one. Even while medical marijuana has its share of opponents, there are a significant number of studies and reports concerning the benefits of the drug.

A new article in Harm Reduction Journal, for example, notes that neuropathic pain affects 5 to 10% of Americans, and that marijuana (cannabis) is effective for treatment of nerve pain without the risk of fatal poisoning, as can occur with opioids. The author suggests doctors who treat patients with neuropathic pain consider a trial of cannabis before prescribing opioids, which may reduce the harm associated with these pain medications.

Aside from physical pain, mental and emotional disorders may be alleviated with medical marijuana use. One use that has demonstrated positive results is in post traumatic stress disorder patients, an area of special concern given the number of Iraq and Afghanistan war veterans with the condition.

New study on marijuana and lung function

It is well accepted that tobacco smoke damages the lungs, but does smoking marijuana cause the same harm? The authors of the new study noted that “marijuana smoke contains many of the same constituents as tobacco smoke,” which suggests the lung damage could be similar.

To answer this question, the research team evaluated the current and lifetime exposure to marijuana and lung function over 20 years in 5,016 men and women who had participated in the Coronary Artery Risk Development in Young Adults (CARDIA) study.

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Fifty-four percent of the participants reported they currently smoked marijuana (795 individuals), tobacco (851), or both (1,065) at one or more examinations during the study period. The intensity of tobacco use was higher (8-9 cigarettes/day) than the intensity of marijuana use (2-3 events within previous 30 days).

Overall, both current and lifetime use of tobacco was associated with a lower FEV1 (first second of expiration), while current smoking was associated with a lower FVC (forced vital capacity). Lower values of both FEV1 and FVC indicate poorer lung function.

FEV1 is the volume of air someone can forcibly blow out of the lungs in one second after having taken a full breath. FVC is the volume of air someone can forcibly blow out after taking a full breath.

Among both current and lifetime marijuana users, FVC was higher, while a higher FEV1 was associated with lifetime exposure. The authors explained it this way: “With up to 7 joint-years of life-time exposure (e.g., 1 joint/day for 7 years or 1 joint/week for 49 years), we found no evidence that increasing exposure to marijuana adversely affects pulmonary function.”

Marijuana users are not off the hook completely, however, when it comes to the effect of the drug on lung function. The researchers also noted a significant decline in FEV1 when use of marijuana reached more than 20 episodes per month.

One possible explanation for the higher FVC in marijuana smokers is that the act of deeply inhaling the smoke stretches their lungs and results in larger lung volumes. Another possibility is the chest wall muscles are strengthened by the inhaling practice of marijuana users, so they perform better on lung function testing.

The authors noted that although their findings suggest occasional marijuana use may not harm lung function, they also “suggest an accelerated decline in pulmonary function with heavy use and a resulting need for caution and moderation when marijuana use is considered.”

Aldington S, Williams M, Nowitz M et al. Effects of cannabis on pulmonary structure, function and symptoms. Thorax 2007; 62(12): 1058-63
Collen M. Prescribing cannabis for harm reduction. Harm Reduction J 2012 Jan; 9:1
Hancox RJ, Poulton R, Ely M et al. Effects of cannabis on lung function: a population-based cohort study. Eur Respir J 2010; 35(1): 42-47
Pletcher MJ, Vittinghoff E, Kalhan R, Richman J, Safford M, Sidney S, Lin F, Kertesz S. Association between marijuana exposure and pulmonary function over 20 years. JAMA 2012; 307(2): 173-81

Picture credit: WIkimedia Commons

Updated February 5, 2014