Over eight sessions, Nguyen used an aerosol monitor to measure the air contaminant levels before and after pot-smoking gatherings. He discovered significantly more contaminants after cannabis smoke than tobacco smoke, specifically particulate matter (PM2.5). According to the study, measurements taken 12 hours after smoking sessions were still above the daily exposure limits set by the U.S. Environmental Protection Agency.
The data is valuable and aligns with similar observational studies on air toxins created by pot smoke. A 2007 study found that marijuana had much higher levels of some of these compounds. Ammonia levels in weed smoke, for example, were 20 times higher than levels measured in tobacco smoke. Hydrogen cyanide, nitric oxide and nitrogen oxides were at concentrations that were three to five times higher than cigarettes. All these chemicals can exacerbate respiratory diseases.
Yet it’s unclear if these higher levels genuinely impact people’s health on par with tobacco. Cigarettes are smoked more regularly than marijuana among U.S. adults, as tracked 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. So the overall exposure and danger from tobacco might still be higher than from pot.
But this relative risk might change over time as weed-smoking becomes more commonplace. American teens, for example, were already 16 times more likely to be daily users of marijuana than cigarettes in the SAMHSA data for 2020.
“It’s just to raise the awareness of a cannabis user that their secondhand smoke from their use can affect the non-smokers, and therefore, they can take some actions to reduce their exposure,” said Hammond from Berkeley.
She and Nguyen see the current moment as analogous to tobacco smoke in the 1980s – before it was discovered to be harmful.
Nguyen and Hammond plan to conduct and release more detailed studies. And the hope for many experts is that the federal government changes its view on cannabis to allow scientists to learn more about the substance. A bill, the Marijuana Opportunity Reinvestment and Expungement Act, or MORE Act, just passed the U.S. House of Representatives. The legislation would decriminalize cannabis, expunge prior 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 reefer madness,” Bekker said. “Some doctors feel even uncomfortable even talking about this stuff.”
The House passed a similar bill in December 2020, but a vote was never taken in the Senate. Such a law would open the doors for a flood of data that could help doctors advise their patients on effective and appropriate uses.
“They’re not sure whether to rub it on their skin or to swallow it, or some vaping or smoke it,” Haney said. “Clinicians don’t have any advice to give because there’s no data there.”