Occasional Marijuana Use Not Tied to Adverse Lung Function

Nonlinear association for marijuana exposure and lung function; no adverse effects for low exposure

TUESDAY, Jan. 10 (HealthDay News) -- Occasional and low cumulative marijuana use does not adversely affect lung function, according to a study published in the Jan. 11 issue of the Journal of the American Medical Association.

Mark J. Pletcher, M.D., M.P.H., from the University of California in San Francisco, and colleagues analyzed current and lifetime exposure to marijuana and pulmonary function using longitudinal lung function and smoking data, collected from 5,115 participants of the Coronary Artery Risk Development in Young Adults study, over 20 years. Lung function was assessed by measurement of the forced expiratory volume in the first second of expiration (FEV1) and forced vital capacity (FVC). The expression of lifetime exposure to marijuana joints was in joint-years, with one joint-year of exposure corresponding to smoking 365 joints or filled pipe bowls.

The researchers found that marijuana exposure was mostly light (median, two to three episodes per month), but was nearly as common as tobacco exposure. Current and lifetime tobacco exposure were linearly associated with reduced FEV1 and FVC. There was a nonlinear association found for exposure to marijuana and pulmonary function. At low exposure levels, there was a 13 mL/joint-year increase in FEV1 and a 20 mL/joint-year increase in FVC. At higher levels of exposure, a leveling or reversal of these associations was seen. At more than 10 joint-years, the slope for FEV1 was −2.2 mL/joint-year, and at more than 20 smoking episodes per month, the slope was −3.2 mL per marijuana smoking episode per month.

"Occasional and low cumulative marijuana use was not associated with adverse effects on pulmonary function," write the authors.

One of the study authors disclosed financial ties to the pharmaceutical industry.

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