The Effects of Secondhand Marijuana Smoke

It was first believed that marijuana smoke is less harmful to you than smoke from tobacco cigarettes, but what if that’s not true? Scientists are performing further testing to see what the effects of second-hand marijuana smoke will do to humans immediately exposed and in the long run.

A study done at the University of California exposed rats to secondhand smoke from marijuana cigarettes and Marlboro cigarettes and studied the effects on blood vessel function. This was performed via a smoking machine in a lab. A test called femoral artery flow-mediated dilation (FMD) was used to measure the rats’ blood vessel function. This test can detect how well the femoral artery carries blood and if it becomes compromised, how long it takes for function in the leg to recover. The results from the test showed, “One minute of exposure to secondhand marijuana smoke impaired flow-mediated dilation (the extent to which arteries enlarge in response to increase blood flow) of the femoral artery that lasted for at least 90 minutes; impairment from 1 minute of secondhand tobacco exposure was recovered within 30 minutes.” The same team also repeated the experiment but without rolling papers and using marijuana with the THC removed. They did this to see if burning the plant itself was the causing the reduction in the arteries rather than the papers of the active ingredients, the same results were found as in the first experiment performed. A limitation of this study is that the dose of smoke is not clear. Researchers don’t know the ambient levels of pot smoke in a given space would be. For this experiment, the levels of smoke can be related to those that can be found at parties or concerts.

A connection between marijuana smoke and lung cancer has not been observed unlike in tobacco smoke. In fact, compounds found in marijuana have been shown to kill cancer cell types like lung, lymphoma, and prostate cancer to name a few. This is not to say that marijuana smoke won't cause cellular damage, Tashkin et al performed a study that did demonstrate that it could cause smoke-induced cellular damage but further proved that there was no link to it causing cancerous cells. Both types of smoke contain carcinogens and matter that can cause an inflammatory response that could lead to an enhancement of carcinogenic effects of smoke. "Nicotine receptors are widely distributed and are found in the epithelial cells lining respiratory passages. Cannabinoid receptors are also widely distributed, but have not been reported in epithelial cells. The differential expression of receptors may account for the apparent difference in carcinogenic activity that results from smoking tobacco compared to cannabis," explains Melamede, who works in the Bioenergetics Institute at the University of Colorado. 

It’s clearly known that second-hand smoke from tobacco is bad for you and we have heard this for decades, however not much has been said about second-hand smoke from marijuana because the studies haven’t been conducted and the results not known, until now. It seems to be that any kind of second-hand smoke, even those promoted as “safer” aren’t necessarily safer because they can still have some cardiovascular risks from the exposure.

Soucres: NIH, Forbes, NCBI