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Is secondhand cannabis smoke bad for you?

Chuck Grimmett/Flickr Creative Commons Attribution-ShareAlike 2.0 Generic (CC BY-SA 2.0)

Most of us don’t even think about the health effects of cannabis secondhand smoke — partly because there’s very little research being done on it.

Yet anti-smoking advocates say any smoke is bad for us and we need to regulate cannabis smoke just like tobacco smoke.

Dr. Matthew Springer was at a Paul McCartney concert a few years ago, when he had an epiphany that sent his career in a new direction.

Something in the air

It happened in the middle of the concert, when people around him started lighting up. A visible haze of pot smoke rose above the audience.


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

That’s when Springer started thinking: San Franciscans would never tolerate cigarette smoke like that anymore. 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 effects of secondhand tobacco smoke. He was already running tobacco smoke tests with cigarettes at his lab at the University of California, San Francisco Medical Center. It wouldn’t be hard to run the same test on cannabis, too.


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


Dr. Springer’s lab at UCSF is not that high tech. There’s a plexiglass chamber with a notch where a cigarette or joint is placed. The smoke fills the chamber and an anesthetized rat, laying with its head sticking just inside the chamber, is exposed to the smoke.


Federal problems


Maybe the most complicated part of Dr. Springer’s work on cannabis is actually getting the pot. Because it’s still federally illegal, he can’t just stroll down the hill to Golden Gate Park.


He has to purchase specially-approved government cannabis. He can’t test on humans; hence, the rats.

(If you’re wondering if the rodents get stoned, Dr. Springer says he doesn’t know.)


His research has shown that the smoke — whether it’s from a cigarette or a joint — affects the ability of the rats’ arteries to grow and shrink. Over time, that causes damage that raises the risk of cardiovascular disease.

“When people think about the bad health effects of tobacco,” Springer says, “The first thing that pops into their mind is cancer.”

Scientists are still debating whether cannabis can cause cancer, but Springer says the majority of deaths from smoking tobacco are actually from cardiovascular problems. So far, his research shows — cannabis could have similar health effects.

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

One would think that the solution is for people just to not smoke, and use vape pens or e-cigarettes instead.

Yet Springer urges caution — those can have their own health effects. Even though they don’t produce secondhand smoke, they still release chemicals in between puffs.

He has yet to study the health effects of “secondhand smoke” from these products — but he says it’s an area that’s ripe for investigation.

None of this work is easy to do since pot is still federally illegal, and that limits funding for research.

Springer worries that in the meantime people might come to the wrong conclusion, that “no news is good news.”

Research gap

“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.

Cynthia Hallett is the president of Americans for Nonsmokers Rights. The organization was established back 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.

Some of the arguments being made in support of cannabis remind Hallett of the arguments made for 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’re prohibited from smoking cannabis anywhere you’re not allowed to smoke tobacco. But Hallett is worried that the legalization of pot could be used to erode those rules.

“It starts on the premise of decriminalization,” she says, 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 says 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 wants to see it regulated that way.

Hallett says we may have to go back to where we were in the ‘70s and ‘80s, and remember etiquette around secondhand smoke.

“It is still polite for you to say, ‘Would you mind not smoking around me?” she says.

To find out what kind of reception that would get, I asked a few regular pot smokers at Magnolia, a cannabis dispensary in Oakland.

“This is the first time that I have heard secondhand smoke in reference to cannabis,” Leigh Crow, a patient-services clerk at Magnolia, admits. “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 says. “I will stop a stranger and say, “You shouldn’t be smoking. My dad died of that!”

But Blaser, like many people, has yet to start thinking about secondhand smoke from cannabis in the same way.

Now that Prop. 64 is in full effect, some of the state tax revenue from the sale of pot will be set aside for cannabis research. The state Occupational Safety and Health board is evaluating workplace hazards specific to the cannabis industry.

With time, there will hopefully be answers so users — and those around them — can make informed decisions.