Thom Morris

This article has been significantly updated to rectify false statements in its initial publication. The Mercury deeply regrets the errors, and thanks Dr. Matthew Springer of the University of California, San Francisco for providing correct information.


Cannabis research is fantastic, and cannabis science is really cool. And it looks like we still need a lot more of both, because right now, results from cannabis studies leave a lot to be desired. Some of them could even be touted by prohibitionists who—surprise, surprise—don’t take all the information into consideration.

That’s the case with a series of ongoing studies recently reported on by NPR’s Morning Edition, which interviewed Matthew Springer, a biologist and cardiology professor at the University of California, San Francisco. In the most San Francisco thing ever, Springer found inspiration at a Paul McCartney concert at AT&T Park, coming to the realization that the people lighting up during the show weren’t smoking cigarettes, but rather—weed! In San Francisco, at a Paul McCartney concert. You’re ruining it for the rest of us, hippies!

Instead of phoning law enforcement or screaming for help, the doctor found inspiration in these rule-defying, counter-culture types. Springer was already performing studies on the effects of secondhand tobacco smoke on rats in his lab at UCSF (he found it made them sing jazz standards in a huskier, sexier voice), and decided to do the same thing with cannabis, using joints to measure the effects of secondhand cannabis smoke.

Springer’s tobacco studies measured the ability of the rats’ arteries to expand after prolonged exposure to smoke. More blood means healthier arteries, but when a person (or a rat) smokes one cigarette after another, the arterial walls can become permanently damaged, causing heart attacks, strokes, and blood clots.

For the cannabis experiment, a lit joint of 0.9 grams was placed into a 21-liter Plexiglas box and mechanically “smoked” for three minutes at the rate of a “puff” every second, filling the box with smoke. Excess smoke was then vented from the chamber to obtain a concentration of smoke equivalent to that which could be found at a party or concert. A ketamine-anesthetized rat was placed into the box, its nose inserted into a gasket, and exposed to the smoke for one minute.

The tobacco study revealed that after 30 minutes, the rat’s arteries would return to their normal function. With cannabis, however, it took 90 minutes—which is also about the length of time it took for write-ups crying “OMG cannabis smoke is three times worse than tobacco smoke!” to show up online.

That's quite a leap, and doesn't take into account the conditions under which the study was conducted.

Look, secondhand smoke is annoying and unhealthy. I don’t ever want to be exposed to secondhand tobacco smoke, and I can understand why some people don’t want to be exposed to secondhand cannabis smoke. (Children shouldn’t be exposed to either kind of smoke—ever.) And yes, there are good methods of enjoying cannabis—such as vaping and eating—that greatly reduce respiratory aggravation and eliminate secondhand smoke. But that’s no reason to stifle social consumption spaces, particularly outdoor sites.

The study NPR reported on is only an introduction to the question of secondhand cannabis smoke. Cannabis science is still in its early days, and remains restrictive and underfunded. While studies like Springer's provide valuable information, we also need to be aware of the conditions in which those studies take place. Re-examining how and where real-world cannabis is consumed may be the best way to give us insight into the real effects of secondhand cannabis smoke.