Is Secondhand Pot Smoke Harmful?

By Shawn Dwyer 11/17/14

New research indicates that second marijuana smoke can be just as bad as tobacco.

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According to preliminary research, secondhand marijuana smoke can potentially be as harmful as secondhand cigarette smoke.

Researchers at the University of California, San Francisco found that the blood vessel function in lab rats dropped by 70% after exposure to marijuana smoke, which resembles the same effect of cigarette smoke.

"Smoke is smoke. Both tobacco and marijuana smoke impair blood vessel function similarly," said the study's senior author, Matthew Springer, a cardiovascular researcher and Associate Professor at the UCSF. "People should avoid both, and governments who are protecting people against secondhand smoke exposure should include marijuana in those rules."

Because both medical and recreational marijuana is becoming legal in more and more states, researchers have amped up their studies of the drug in order to understand the effects of a drug that has, up until now, remained somewhat benign.

"Marijuana for a long time was viewed as a relatively innocuous drug, but a lot of that came from a lack of information," said Dr. Stephen Thornton, a toxicologist and Medical Director of the Poison Control Center at the University of Kansas Hospital. "Now, as more and more people are using it, we're finding more and more detrimental effects. People just need to be cautious."

For the study, researchers measured blood vessel dilation 10 minutes before and 40 minutes after exposure to marijuana smoke. While rats in previous studies showed that their blood vessel dilation returned to normal after being exposed to cigarette smoke, the blood vessels in the rats exposed to weed had not returned to normal even after 40 minutes, leading researchers to conclude that secondhand marijuana smoke might even have more detrimental effects than tobacco smoke.

"Tobacco smoke and marijuana smoke both contain thousands of chemicals, many of which are toxic," said Springer. "Some of [the new] laws might be written very narrowly [with this in mind]."

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Shawn Dwyer is a writer, editor and content producer living in Los Angeles. You can find him on Linkedin.