Are There Risks From Secondhand Marijuana Smoke? Early Science Says Yes

Written by MARISSA ORTEGA-WELCH, March 19, 2018 -

[MORNING ADDITION: NPR .org]

The inspiration arrived in a haze at a Paul McCartney concert a few years ago in San Francisco.

"People in front of me started lighting up and then other people started lighting up," says Matthew Springer, a biologist and professor in the division of cardiology at the University of California, San Francisco. "And for a few naive split seconds I was thinking to myself, 'Hey, they can't smoke in AT&T Park! I'm sure that's not allowed.' And then I realized that it was all marijuana."

Recreational pot was not legal yet in the state, but that stopped no one. "Paul McCartney actually stopped between numbers and sniffed the air and said, 'There's something in the air — must be San Francisco!' " Springer recalls.

As the visible cloud of pot smoke took shape, so did Springer's idea to study the effects of secondhand marijuana smoke.

He started thinking: San Franciscans would never tolerate those levels of cigarette smoke in a public place anymore. So why were they OK with smoke from burning pot? Did people just assume that cannabis smoke isn't harmful the way tobacco smoke is?

Springer was already researching the health effects of secondhand tobacco smoke on rats at his lab at UCSF. He decided to run the same tests using joints.

"By the time I left the concert, I was resolved to at least try to make this happen," he says.

He knew it would be difficult. Marijuana is still an illegal drug under federal law, and Springer's research uses federal funds; so he has to purchase specially approvedgovernment cannabis for study. He also can't test it on humans; hence, the rats.

In the lab, Springer puts a cigarette or a joint in a plexiglass box. Then he lights it, and lets the chamber fill with smoke, where an anesthetized rat is exposed to the smoke.

So far, Springer and his colleagues have published research demonstrating that secondhand smoke makes it harder for the rats' arteries to expand and allow a healthy flow of blood.

With tobacco products, this effect lasts about 30 minutes, and then the arteries recover their normal function. But if it happens over and over — as when a person is smoking cigarette after cigarette, for example — the arterial walls can become permanently damaged, and that damage can cause blood clots, heart attack or stroke.

Springer demonstrated that, at least in rats, the same physiological effect occurs after inhaling secondhand smoke from marijuana. And, the arteries take 90 minutes to recover compared to the 30 minutes with cigarette smoke.

Springer's discovery about the effect on blood vessels describes just one harmful impact for nonsmokers who are exposed to marijuana. Statewide sampling surveys of cannabis products sold in marijuana dispensaries have shown that...

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(CURATED CONTENT: This story is part of NPR's reporting partnership, local member stations and Kaiser Health News. Written by MARISSA ORTEGA-WELCH, March 19, 2018 - [NPR.org])

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