Fact Check: Is bong smoke really as harmful as secondhand cigarette smoke?

Over eight sessions, Nguyen used an aerosol monitor to measure airborne contaminant levels before and after gatherings of pot smokers. He discovered many more contaminants after cannabis smoke than tobacco smoke, especially particulates (PM2.5). According to the study, measurements taken 12 hours after smoking sessions were still above daily exposure limits set by the US Environmental Protection Agency.

The data is valuable and aligns with similar observational studies of airborne toxins created by pot smoke. A 2007 study found that marijuana had much higher levels of some of these compounds. Ammonia levels in cannabis smoke, for example, were 20 times higher than levels measured in tobacco smoke. Hydrogen cyanide, nitric oxide and nitrogen oxides were in concentrations three to five times higher than cigarettes. All of these chemicals can exacerbate respiratory illnesses.

Still, it’s unclear whether these higher levels have any real impact on people’s health in the same way tobacco does. Cigarettes are smoked more regularly than marijuana among American adults, as reported by the Substance Abuse and Mental Health Services Administration. According to SAMHSA data, about 24.8 million adults smoked cigarettes daily or almost daily in 2020, compared to 14.6 million adults who used marijuana regularly. Thus, the overall exposure and danger of tobacco could still be higher than that of pot.

But that relative risk could change over time as smoking weed becomes more common. American teenagers, for example, were already 16 times more likely to be daily users of marijuana than cigarettes in SAMHSA data for 2020.

“It’s just to make a cannabis user aware that secondhand smoke from their use can affect non-smokers, and therefore they can take some steps to reduce their exposure,” Berkeley’s Hammond said.

She and Nguyen see the current moment as analogous to the tobacco smoke of the 1980s – before it was discovered to be harmful.

Nguyen and Hammond plan to conduct and publish more detailed studies. And the hope of many experts is that the federal government will change its views on cannabis to allow scientists to learn more about the substance. A bill, the Marijuana Opportunity Reinvestment and Expungement Act, or MORE Act, has just been passed by the United States House of Representatives. The legislation would decriminalize cannabis, erase previous convictions and make the drug more accessible for study.

“There’s a certain stigma attached to this thing and years of propaganda — that it’s freezing madness,” Bekker said. “Some doctors even feel uncomfortable even talking about this stuff.”

The House passed a similar bill in December 2020, but there was never a vote in the Senate. Such a law would open the doors to a flood of data that could help doctors advise their patients on effective and appropriate uses.

“They don’t know whether to rub it on their skin or swallow it, or vape it or smoke it,” Haney said. “Clinicians have no advice to give because there is no data.”

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