January 24, 2018
Smoking Marijuana Joint
Wellness Tip

Risks of Secondhand Marijuana Smoke

by Jeanine Barone  

It’s well known that secondhand tobacco smoke is harmful. But there’s been little research into the effects of exposure to secondhand smoke from marijuana, which is now legal for medical use in 24 states plus the District of Columbia—and legal in four states (plus D.C.) for recreational use. Should smoke-free laws include marijuana, to protect bystanders from potential adverse effects of inhaling it? A new study suggests they should—and that people with cardiovascular disease in particular may be at heightened risk from breathing in marijuana smoke.

In the study, published in the Journal of the American Heart Association, researchers from the University of California, San Francisco, found that exposing rats to just one minute of secondhand marijuana smoke significantly impaired the ability of blood vessels to dilate (widen), which could impair blood flow to the heart and promote atherosclerosis. The effect was similar to that of secondhand tobacco smoke, which is known to increase cardiovascular risk. What’s more, it took the blood vessels far longer to return to normal after the marijuana smoke exposure compared with tobacco smoke. Although the mechanism by which secondhand smoke from marijuana impairs blood vessels isn’t totally clear, it may increase the production of free radicals as well as impair the production of nitric oxide, a chemical vital for blood vessel functioning.

While the findings come from animals and not humans, they’re important because some people assume that marijuana smoke is benign, or at least not as damaging as cigarette smoke. This study suggests that marijuana’s effect on blood vessels is at least as deleterious as that of tobacco smoke. And while the effect observed in the study was temporary, “other research has shown that frequent exposure to secondhand tobacco smoke over time can lead to chronic blood vessel dysfunction, which can increase the risk of cardiovascular disease,” says Matthew Springer, PhD, an author of the study and professor of medicine in the Division of Cardiology at UCSF. Even the temporary dysfunction may increase the risk of heart attack and stroke, Springer added, especially in people who have cardiovascular disease.

Bottom line:

As marijuana use increases, so do concerns about the effects of exposure to secondhand marijuana smoke. Emerging evidence suggests that, far from benign, secondhand marijuana smoke may have the same adverse cardiovascular effects as secondhand tobacco smoke. If your doctor prescribes marijuana for a medical condition, ask about nonsmoking forms of cannabis, such as marijuana cookies or other edibles. As we've said before, no smoke is good smoke.

Also see Marijuana: Hazy Health Risks and Secondhand Smoke: Still a Killer.