Secondhand Weed Smoke Might Be Way More Harmful Than We Thought

You may want to leave the room the next time your stoner friends pass the dutchie on the left hand side.

It turns out that secondhand marijuana smoke can have some pretty serious health consequences.

At least, that’s what a new study involving rats has revealed.

When exposed to only one minute of secondhand marijuana smoke, the rats’ blood vessels took at least three times longer to recover function, compared to recovery after a minute of breathing secondhand tobacco smoke.

Researchers examined blood vessel function in rats before and after exposure to secondhand marijuana smoke at levels similar to real-life secondhand tobacco smoke.

The research – published in Journal of the American Heart Association, the Open Access Journal of the American Heart Association/American Stroke Association – revealed that the rats’ arteries carried blood less efficiently for at least 90 minutes after exposure to secondhand marijuana smoke.


Most notably, similar exposure to secondhand tobacco smoke caused blood vessel impairment that recovered within 30 minutes.

“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, Ph.D., study senior author and professor of medicine at the University of California, San Francisco’s Division of Cardiology.

According to researchers, it is the mere burning of the plant material that appears responsible for the impaired blood vessels, as opposed to chemicals like nicotine or THC or the rolling paper.

Of course, it’s important to note that the study involved rats and not humans. Even so, the results are telling.

“Arteries of rats and humans are similar in how they respond to secondhand tobacco smoke, so the response of rat arteries to secondhand marijuana smoke is likely to reflect how human arteries might respond,” said Springer.


It’s important information to consider at a time when dispensaries seem to pop up every week in Toronto.

“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.”

The researchers stress that the inhalation of smoke should be avoided – regardless of whether it comes from tobacco or marijuana.

It seems surprising that this is the first study of its kind. One thing is for sure – it probably won’t be the last.

After all, it doesn’t look like the cannabis craze is going up in smoke anytime soon.