According to findings presented Nov. 16 at the American Heart Association scientific sessions in Chicago, endothelial function was just as impaired in rats exposed to second-hand smoke from marijuana as cigarettes.

Blood vessel function remained impaired even when the marijuana contained no tetrahydrocannabinol (THC). THC is the compound that produces the feeling of intoxication in humans.

Researcher Matthew L. Springer, PhD, of the Center for Tobacco Control Research & Education at the University of California, San Francisco, told Cardiovascular Business, “The take home message is that smoke is smoke. Whether you’re getting it from tobacco or marijuana, you’re getting smoke. If you’re smoking it yourself, you’re getting smoke. If you’re a bystander exposed to someone else’s second-hand smoke, you’re getting smoke.”

Using rat models, Springer and colleagues found that arterial function was impaired by 50 percent to 70 percent when exposed to marijuana second-hand smoke for about 30 minutes. They noted that the most exposure occurred during the first 10 minutes. One concerning finding included that while tobacco second-hand smoke impairment typically resolves after 30 minutes after exposure, marijuana exposure took much longer.

The rats were exposed to levels of marijuana smoke found in real-world tobacco smoke exposure settings. Although exposures may currently be different in social settings where marijuana is used, Springer warned that more and more nonsmokers will be exposed to greater quantities as laws on marijuana use change--particularly, if public smoking laws aren’t written broadly enough to ensure marijuana is included.

“With marijuana being legalized in more and more states, there will be more and more occasions for the public to be exposed to second-hand smoke from marijuana,” Springer stated. “As governments write their smoke-free laws and the laws that limit the smoking of cigarettes in public places, they need to include marijuana in them.”

In tobacco smoke, Springer and colleagues have shown that even at very low levels of exposure, impairment happens. “Even after exposing rats to tobacco smoke for only one minute of real-world exposure levels, we were able to detect impairment in blood vessel function.” Springer noted that with the similarities in endothelial function results in mind, what happens for marijuana smoke can also be extrapolated even at low levels.

Springer reminded physicians that in the changing public setting, marijuana is not just a drug anymore. Patients should be screened for exposure to marijuana equally as to exposure to cigarettes.  Springer also noted that physicians should emphasize avoiding second-hand smoke from cigarettes, cigars and marijuana in conversations with patients.

An estimated 53,000 U.S. deaths per year are caused by second-hand smoke; around 34,000 of those are from second-hand smoke-related heart disease, according to the U.S. surgeon general. It is unknown how many of these deaths are related to exposure to marijuana second-hand smoke.

Springer added that for any combustible material, thousands of toxic by-products are released. While the specific components causing endothelial function to change are not known, several are suspected and currently being researched. Future research, Springer noted, will include determining what has the most impact on endothelial function.