Exposure to secondhand tobacco smoke kills nearly 900,000 non-smokers every year. And now, under the impression that legalization has increased the number of public tokers, non-smokers and smokers alike are starting to point fingers at secondhand weed smoke, too.
You can understand the concern, considering the awful impact secondhand cigarette smoke has had — and will continue to have — on so many people. But is secondhand weed smoke actually all that dangerous? Let’s look at the facts.
It Might Screw With Your Blood Vessels
A 2016 rat study conducted at the University of California, San Francisco, found that secondhand smoke from both cannabis and tobacco briefly prevents arteries from expanding in order to allow for healthy blood flow. The arteries recover 90 minutes after being exposed to secondhand weed smoke (compared to only 30 minutes with secondhand cigarette smoke), but when this happens repeatedly — say, you’re lounging next to a chainsmoker (or chaintoker) — the arterial walls can become permanently damaged. Worse yet, this damage can result in blood clots, heart attack and/or stroke.
These results aren’t exactly surprising, considering the lengthy list of toxic substances found in smoke (cannabis or otherwise): A 2008 study found that weed smoke actually contains significantly higher levels of certain toxins — including ammonia and hydrogen cyanide — than tobacco smoke (although, recently implemented regulations may reduce the amount of contaminants found in cannabis and the smoke caused by it).
That said, Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (NORML), emphasizes the fact that this particular study assessed rats, and therefore, it doesn’t accurately explain how weed smoke effects humans. “Longitudinal studies in humans haven’t replicated these results,” he says. And science corroborates his claim: A 2017 study found that lifetime marijuana use isn’t associated with an increased incidence of cardiovascular disease (including blood clots, heart attack and/or stroke).
It Won’t Give You Lung Cancer
“Direct cannabis smoke exposure, even long-term, isn’t associated with the sort of adverse health effects typically associated with tobacco — such as lung cancer and COPD [chronic obstructive pulmonary disease],” Armentano explains. “Therefore, it’s sensational to presume that secondhand exposure poses a significant public safety risk.”
Once again, he’s right about secondhand weed smoke not causing lung cancer or COPD — at least per a 2013 study performed by Donald Tashkin, an emeritus professor of medicine at UCLA in the Division of Pulmonary and Critical Care Medicine and author of numerous articles on marijuana and lung health. Tashkin previously explained why weed smoke doesn’t cause chronic lung disease to my colleague Tierney Finster:
“The THC in marijuana binds to cannabinoid-type 1 receptors that are expressed on the vagal nerve endings in the lungs. And when these receptors are bound by THC, the THC inhibits the release of a chemical that’s responsible for bronchoconstriction called acetylcholine. It’s a very comparable process to what happens with use of the medicines that are currently available for prescription to treat bronchospastic diseases right now.”
Weed smoke does, however, increase the risk of developing a chronic cough (sometimes called smoker’s cough) and excess phlegm production when inhaled directly, so it’s fair to say that secondhand weed smoke may pose that same threat to non-smokers.
It Can Get You High…
…but you’d have to be seriously hot-boxed for that to happen. A 2015 study found that, “under extreme, unventilated conditions, secondhand cannabis smoke exposure can produce detectable levels of THC in blood and urine, minor physiological and subjective drug effects and minor impairment on a task requiring psychomotor ability and working memory.” In other words, don’t expect to get a contact high if you’re standing next to a few tokers at a rock show, but do expect to get a contact high if you’re squished between a few tokers in the backseat of a VW Bus.
All of this, however, becomes even less worrisome when you consider combustion-free delivery methods, like vaping. “Vaporization, which heats marijuana to a point where cannabinoid vapors form, mitigates consumer’s exposure to potential respiratory hazards, such as the inhalation of combustive smoke or exposure to unwanted particulate matter,” Armentano says, providing study after study to back up his claim.
Still, while all the current research suggests that secondhand weed smoke is far less hazardous than secondhand tobacco smoke, you should still be considerate when smoking around others. After all, no one likes smelling like day-old bong water.