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Now That Pot Is Legal, Should You Worry About Secondhand Smoke? California Scientist Says Yes

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A woman from Seattle smokes a joint at the first annual DOPE Cup, a cannabis competition in Portland, Oregon, on Oct. 4, 2015. (Josh Edelson/AFP/Getty Images)

Commercial sales of cannabis to recreational users began Jan. 1 in California. It hasn't been even two months in this brave new world, but new questions about marijuana's health impacts are already popping up. Is smoking cannabis bad for your health? If so, how bad? And are we talking physically or mentally? What about secondhand smoke?

One scientist at University of California San Francisco decided to tackle that last question after attending a Paul McCartney concert a few years ago.

Matthew Springer doesn't remember what song the former Beatle was playing when he had a research epiphany, but he does remember that it happened when dozens of fans decided it was that time during the concert when it might be good to "toke up."

A visible haze of pot smoke rose above the audience.

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


“Paul McCartney actually stopped between numbers and sniffed the air and said, ‘There's something in the air — must be San Francisco!’ ” he recalled.

And that’s when Springer started thinking: San Franciscans would never tolerate those levels of cigarette smoke anymore. So why were they OK with pot smoke? Did people just assume that cannabis smoke isn’t harmful the way tobacco smoke is?

Like any good scientist, he wondered: Is that true? Or is secondhand smoke from cannabis bad for us?

While anyone might have been able to ask these questions, Dr. Springer is one of the few people in the world who could actually answer them.

He’s a pre-eminent researcher on the health effects of secondhand tobacco smoke. He was already running tests on rats, using cigarettes, at his lab at UCSF. Maybe he could 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 said.

He knew it wouldn’t be easy. Because pot is still illegal under federal law, and Springer's research uses federal funds, he can’t just stroll down the hill and buy some from a dispensary, or from someone in Golden Gate Park. He has to purchase specially approved government cannabis and he can’t test on humans; hence, the rats.

In the lab, Springer puts a cigarette or joint in a plexiglass box. Then he lights it, and the chamber fills with smoke. An anesthetized rat, laying with its head sticking just inside the chamber, is exposed to the smoke.

(If you’re wondering if the rodents ever get stoned, Springer said he doesn’t know, and anyway, they're asleep.)

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, because a person is smoking cigarette after cigarette, the arterial walls can become permanently damaged, and that damage can cause blood clots, heart attack or stroke.

Springer demonstrated that the exact same physiological effect occurs after inhaling secondhand smoke from marijuana. Not only that, the arteries take 90 minutes to recover -- three times as long, compared to the 30 minutes with cigarette smoke.

Springer's discovery describes just one harmful impact for non-smokers exposed to marijuana smoke. Statewide sampling surveys of cannabis products sold in marijuana dispensaries have shown that cannabis products may contain dangerous bacteria or mold, or residues from pesticides and solvents.

California law does requires testing for these contaminants, but the regulations are being rolled out in three phases over the course of 2018. And since much of the marijuana being sold now was harvested last fall, consumers will have to wait until early 2019 before they can purchase products that have been fully tested according to state standards.

“People think cannabis is fine because it's 'natural,' ” Springer said. “I hear this a lot. I don't know what it means.” He concedes that tightly regulated marijuana, which has been fully tested, doesn’t have as many chemical additives as cigarettes.

But even if the cannabis tests clean, you’re still inhaling smoke, Spring emphasized, and smoke itself is bad for your lungs, heart and blood vessels. And that's just cardiovascular effects -- other researchers are still exploring the relationship between marijuana smoke and long-term cancer risk.

“People should think of this not as an anti-THC conclusion, but an anti-smoke conclusion,” Springer said.

So is the solution simply to avoid smoke from combustion per se, by eating cannabis-infused products, or using "smokeless" e-cigarette or vaping devices?

Springer still urges caution,  because vaping can have its own health effects. Even though vaping devices don’t produce smoke from combustion, they do release a cloud of aerosolized chemicals. Springer is studying the health effects of those chemicals, too.

All this research takes time. Meanwhile, Springer worries that people might come to the wrong conclusion, that "no news is good news."

“We in the public health community have been telling them for decades to avoid inhaling secondhand smoke from tobacco,” Springer says. “We have not been telling them to avoid inhaling secondhand smoke for marijuana, and that's not because it's not bad for you, it's because we just haven't known. The experiments haven't been done.”

Anti-smoking campaigners say we can’t afford to wait until the research is complete. Recreational pot is already a reality.

Cynthia Hallett is the president of Americans for Nonsmokers' Rights, based in Berkeley. The organization was established in 1976, before there was a lot known about the health effects of secondhand smoke from tobacco.

Now that cannabis is becoming more common across the country, her organization is taking it on.

Hallett said some of the arguments being made in support of cannabis remind her of the arguments made on behalf of tobacco decades ago.

“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 told me. “The tobacco companies used to say the same thing about tobacco cigarettes.”

In California, you are prohibited from smoking cannabis anywhere where you’re not allowed to smoke tobacco -- that includes schools, airplanes and most workplaces. But Hallett is worried that the legalization of pot could be used to erode those rules.

“It starts on the premise of decriminalization,” she said, and then over time there’s “a chipping away at strong policies.”

A lot of cannabis advocates want to see pot regulated like alcohol. They want cities to issue permits for specialized smoking lounges, similar to wine bars.

But Hallett pointed out that smoke drifts and affects workers in a way that alcohol doesn’t.

"The difference is, if I were to spill my beer on you in a bar, it wouldn’t affect your long-term health. If I choose to smoke, it can affect the health of the person near me."

Pot is more like tobacco in that respect — and Hallett said it should be regulated that way, at all times.

Hallett believes many pot smokers are still in denial -- after fighting so hard for legalization, it’s hard to admit there are potential harms. She said this time in California culture brings to mind a similar time in the 1970s and '80s, when Americans started demanding more regulations for secondhand smoke, and a new etiquette around smoking took form.

When it comes to marijuana, Hallett said, “it is still polite for you to say: ‘Would you mind not smoking around me?' "

At Magnolia, a cannabis dispensary in Oakland, a reporter asked some regular pot smokers about what responsibilities -- if any -- they should have when it came to nearby nonsmokers.

“This is the first time that I have heard secondhand smoke in reference to cannabis,” admitted Lee Crow, a patient-services clerk at Magnolia. “I’ve tried to be courteous, just common courtesy like with anything.”

That was the case for most of the people I talked to at Magnolia. Even the dispensary’s director of clinical services, Barbara Blaser, admits she thinks a lot about secondhand smoke from cigarettes, but not pot.

“Both of my parents died of lung cancer!” she said. “I will stop a stranger and say, 'You shouldn’t be smoking. My dad died of that!' ”

But Blaser, like many cannabis consumers, hasn't  really started thinking about the health impacts of cannabis smoke -- much less its secondhand smoke -- in quite the same way.

Proposition 64 calls for some of the state tax revenue from the sale of pot to be distributed to cannabis researchers. In addition, the state Occupational Safety and Health Standards Board is examining workplace hazards that are specific to the cannabis industry.

Californians might have already legalized pot, but have only just begun to explore the science behind the smoke and to create a new etiquette for how to handle it. 

Additional reporting by KQED Health Editor Carrie Feibel. 


A version of this story first aired on KALW’s Crosscurrents.

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