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Secondhand marijuana smoke may be worse than secondhand tobacco smoke, research shows

Research shows that it may take longer for arteries to recover form secondhand marijuana smoke than from secondhand tobacco smoke. (Justin Sullivan/Getty Images)

Exposure to secondhand pot smoke may be even more dangerous for your health than secondhand tobacco smoke, according to a California researcher who has been studying the effects of both.

Matthew Springer, a biologist and professor in the cardiology division at the University of California, San Francisco, tested the effects of secondhand marijuana smoke and found it takes three times longer for lab rats' arteries to recover from pot smoke than from tobacco smoke, Kaiser Health News reported.

Why did Springer decide to test secondhand marijuana smoke?

Springer attended a concert a few years ago where people were lighting up joints in a public space where cigarette smoking wasn't allowed.

Most San Franciscans would not tolerate smoking cigarettes in public spaces and wondered why they were OK with smoking marijuana in those same spaces.

"Did people just assume that cannabis smoke isn’t harmful the way tobacco smoke is?" Springer wondered.

He was already testing the health effects of secondhand tobacco smoke on rats at his lab, so he decided to run the same tests using pot.

“People think cannabis is fine because it’s ‘natural,'” Springer told KHN. “I hear this a lot. I don’t know what it means.”

How was the research conducted?

Springer placed a cigarette or a joint in a plexiglass box and lit it. He allowed the box to fill up with smoke before venting most of it out, which simulated being around a smoker.

He then exposed an anesthetized rat to the smoke for one minute.

Research published by Springer's lab showed that only one minute of exposure to secondhand smoke makes it more difficult for the rats' arteries to expand and have healthy blood flow.

The rats exposed to tobacco smoke took about 30 minutes for their arteries to recover whereas the rats exposed to marijuana smoke took about 90 minutes to recover.

Repeated exposure can cause permanent damage and lead to blood clots, heart attack or stroke, Springer said.

Because Springer’s research uses federal funds, he had to purchase specially approved government cannabis for study, and he couldn't test on humans.

Are there other harmful effects?

The effect on blood vessels may not be the only harmful impact on the health of nonsmokers.

In California, a sampling of cannabis products sold in dispensaries showed many items contain dangerous mold or bacteria, or residues from pesticides and solvents, according to Kaiser.

Even if the marijuana is found to be clean from contaminants, all smoke is bad for the lungs, heart, and blood vessels, Springer said.

“People should think of this not as an anti-THC conclusion,” he said, referring to the active ingredient in marijuana, “but an anti-smoke conclusion.”

What else?

Some of the arguments surrounding secondhand pot smoke remind Cynthia Hallett, president of Americans for Nonsmokers’ Rights, of the same arguments made many years ago about tobacco.

“I’m seeing a parallel between this argument that, ‘Gee, we just don’t have a lot of science and so, therefore, let’s wait and see,'” Hallett said. “The tobacco companies used to say the same thing about tobacco cigarettes.”

Pot smoking is not permitted anywhere tobacco smoking prohibited, but Hallett is afraid that could change.

She said it starts with decriminalization. Then, over time, there’s “a chipping away at strong policies.”

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