With the increased acceptance and legalization of marijuana in many parts of the world, studies are now trying to determine its effects on health. Although many think of marijuana smoke as less harmful than tobacco smoke, a new study suggests that secondhand smoke poses dangers to our cardiovascular system whether it stems from marijuana or tobacco.

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The study found that in laboratory rats exposed to secondhand smoke from a marijuana cigarette, blood vessels had difficulty widening, much like the vessels in rats who were exposed to secondhand tobacco smoke.

“While the effect is temporary for both cigarette and marijuana smoke, these temporary problems can turn into long-term problems if exposures occur often enough and may increase the chances of developing hardened and clogged arteries,” said Matthew Springer, professor of medicine at the University of California and senior author of the study.

In addition, the data revealed that rats exposed to marijuana smoke for one minute took 90 minutes to recover fully, approximately three times as long as rats that were exposed to tobacco smoke. However, when the researchers removed tetrahydrocannabinol (THC) from the marijuana cigarettes, the blood vessel disruption was still observed, suggesting that it is the burning smoke rather than the active components of marijuana responsible for the narrowing of the rats’ blood vessels.

As of now, long-term studies on the effects of marijuana on cardiovascular function are limited, especially when it comes to secondhand smoke. There is even some evidence that although inhaling marijuana poses immediate and temporary cardiovascular risks, its modulation of the endocannabinoid system can actually slow down the development of atherosclerosis. Additional long-term research will need to be conducted to get a final answer on the exact negative effects of marijuana smoke.

“There is widespread belief that, unlike tobacco smoke, marijuana smoke is benign,” Springer said. “We in public health have been telling the public to avoid secondhand tobacco smoke for years, but we don’t tell them to avoid secondhand marijuana smoke, because until now we haven’t had evidence that it can be harmful.”

“Increasing legalization of marijuana makes it more important than ever to understand the consequences of exposure to secondhand marijuana smoke,” the team concluded. “It is important that the public, medical personnel, and policymakers understand that exposure to secondhand marijuana smoke is not necessarily harmless.”

Journal Reference: One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function. 27 July 2016. 10.1161/JAHA.116.003858