Dangers of Secondhand Marijuana Smoke

Chicago—According to the 2014 Surgeon General’s report on the consequences of smoking, secondhand tobacco smoke causes about 34,000 premature deaths from heart disease each year in the United States among nonsmokers. Secondhand marijuana smoke may have similar cardiovascular effects as tobacco smoke, according to preliminary research on rats presented by Matthew Springer, PhD, at the AHA meeting.

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“Most people know secondhand cigarette smoke is bad for you, but many do not realize that secondhand marijuana smoke may also be harmful,” said Dr. Springer, senior author of the study, cardiovascular researcher, professor of medicine, University of California, San Francisco, in a press statement.

Marijuana and tobacco smoke are chemically and physically alike, aside from their active ingredients (nicotine and tetrahydrocannabinol [THC]). In the study, Dr. Springer and colleagues evaluated whether short exposure to marijuana secondhand smoke causes acute vascular endothelial dysfunction similar to that of tobacco secondhand smoke. Exposure to tobacco secondhand smoke impairs arterial flow-mediated dilation (FMD) in humans and rats.

The researchers used an FMD model and exposed anesthetized rats (n=8) to marijuana smoke using a modified cigarette smoking machine. They measured FMD at baseline, 10 minutes after the end of exposure, and 40 minutes after the end of the exposure. FMD was measured by micro-ultrasound measurements of femoral artery diameter before and after transient surgical occlusion of the common iliac artery.

The findings showed that arterial function decreased 50% to 70% after 30 minutes of exposure to secondhand marijuana smoke. In previous tobacco studies, blood vessel function tended to return to normal within 30 minutes of exposure; however, in this study, blood vessel function did not return to normal when measured 40 minutes after exposure.

The researchers found that marijuana secondhand smoke starting at 667 mcg/m3 respirable suspended particles (RSP) <2.5 micrometers caused FMD to fall from 7.5% at baseline to 2.3% after 10 minutes, and 2.2% after 40 minutes. Even when marijuana contained no THC, blood vessel function was still impaired. Secondhand smoke from placebo marijuana lacking THC starting at 671 mcg/m3 RSP impaired FMD (9.9% at baseline, 4.3% after 10 minutes, and 5.5% after 40 minutes), “confirming that impairment did not depend on the THC,” according to the study.

“Marijuana and tobacco secondhand smoke impair endothelial function similarly under comparable exposure conditions,” the researchers concluded. “Public exposure to secondhand smoke should be avoided whether the source is tobacco or marijuana.”—Eileen Koutnik-Fotopoulos