Is Secondhand Marijuana Smoke Dangerous?

By John Lavitt 08/03/16

A recent NIDA study examined whether secondhand marijuana smoke had the same dangerous effects as secondhand tobacco smoke. 

Is Secondhand Marijuana Smoke Dangerous?

Recent findings of a National Institute on Drug Abuse-funded animal study found that marijuana smoke opens the door to unexpected cardiovascular risks. The initial findings suggest that secondhand marijuana smoke may cause longer-lasting cardiovascular harm than secondhand tobacco smoke. Although people joke about getting a contact high after being caught in a cloud of pot smoke, the study found that this may not come without certain risks.

In the pre-human study on rats, University of California at San Francisco (UCSF) researchers exposed the animals to moderate-to-high levels of secondhand marijuana or tobacco smoke—the rough equivalent of the amount of secondhand smoke in a restaurant that allows smoking. Although one minute of exposure to secondhand smoke from pot diminishes blood vessel function to the same degree as tobacco, the cardiovascular effects last three times longer with pot. 

As reported on in a recent issue of the Journal of the American Heart Association, all secondhand smoke impairs blood vessel function by hampering flow-mediated dilation (FMD). FMD describes the extent to which arteries dilate when blood flow is increased. When FMD is hampered, the body's ability to deliver blood to the brain and the rest of the body is limited, and cardiologists view such a state as a red flag for potential heart problems like heart attacks. Although secondhand smoke from marijuana and tobacco hampered FMD similarly at first, the effects on FMD caused by pot smoke lasted three times as long. 

UCSF’s Matthew Springer, professor of medicine and senior author of the study, explained, “The biggest reason that people believe marijuana secondhand smoke is harmless is because the public health community hasn’t had direct evidence of its harmful effects like it does with tobacco … At this point, we’re saying that inhaling any smoke is detrimental to your health. I think that people should avoid inhaling smoke whether it’s from tobacco or marijuana cigarettes, forest fires, barbecues—just avoid smoke.”

However, more research is needed to validate the findings in a human model. Without human studies, it can’t be confirmed that the FMD response is the same as in the rats. The question is, just how much risk does marijuana smoke raise for non-smokers in enclosed spaces? “Our findings in rats suggest that SHS can exert similar adverse cardiovascular effects regardless of whether it is from tobacco or marijuana,” concludes the research team. 

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Growing up in Manhattan as a stutterer, John Lavitt discovered that writing was the best way to express himself when the words would not come. After graduating with honors from Brown University, he lived on the Greek island of Patmos, studying with his mentor, the late American poet Robert Lax. As a writer, John’s published work includes three articles in Chicken Soup For The Soul volumes and poems in multiple poetry journals and compilations. Active in recovery, John has been the Treatment Professional News Editor for The Fix. Since 2015, he has published over 500 articles on the addiction and recovery news website. Today, he lives in Los Angeles, trying his best to be happy and creative. Find John on Facebook, Twitter, and LinkedIn.