Inhaling marijuana second-hand smoke inhibits the arteries’ ability to expand properly, mirroring the effects of second-hand tobacco smoke. With such findings in mind, public safety regulations on cannabis use in public ought to mirror those for tobacco, i.e. no smoking indoors.

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It’s more of a smoke problem than a cannabis one

Matthew Springer, a biologist and professor in the division of cardiology at the University of California, San Francisco, recently spoke to NPR about the often ignored effects of second-hand marijuana smoking. He argues that Californians, and San Franciscans in particular, are very intolerant to smoking cigarettes in public, as they should be. But when it comes to smoking marijuana, people are far more lenient. Was the public’s impression that just because there was no research or debate about the potential hazards of marijuana second-hand smoke, then it must be benign? At his UCSF lab, Springer already had experience studying the effects of tobacco-second smoke in rats, when he decided to do the same for marijuana.

Last year, Spring and colleagues published a paper showing that exposure to marijuana second-hand smoke has the same physiological effects as second-hand smoke from tobacco. The research showed that the rats’ arteries lost some of their ability to expand and allow a healthy flow of blood. This effect lasted for 30 minutes after exposure. The arteries took 90 minutes to recover compared to the 30 minutes with cigarette smoke.

“People think cannabis is fine because it’s ‘natural,’ ” Springer told NPR. “I hear this a lot. I don’t know what it means.”

Spring says that smoke itself is bad for the lungs, heart and blood vessels. Currently, other researchers are exploring associations between smoking cannabis and cancer. He also urges caution around vaping, which although doesn’t generate combustible products (smoke), it still releases a cloud of aerosolized chemicals. The effects of such chemicals is still a subject of research.

“We in the public health community have been telling them for decades to avoid inhaling secondhand smoke from tobacco,” Springer said. “We have not been telling them to avoid inhaling secondhand smoke from 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.”

Cannabis is still illegal at the federal level in the United States, but more than 20 cities or states have legalized it in one way or another. Not too long ago, marijuana use was severely stigmatized by a society which unfairly saw no medical use whatsoever to cannabis and put it at the same level of hazard with hard drugs. To this day, marijuana is classed as a schedule 1 drug, at the same level with heroin, LSD, ecstasy, methaqualone, and peyote. Drugs like cocaine and methamphetamine are schedule II substances, meaning they have a lower potential for abuse than marijuana. Such classifications, which were established in the 1970s by the Nixon administration and have changed very little since then, are largely arbitrary and certainly not based on science, at least not in the case of marijuana.

Against this backdrop of prohibition and stigma, a counter-culture emerged which fought back to redeem marijuana’s reputation in the eye of the public. The cultural shift towards marijuana has been the backbone that enabled the legislature changes of the past decade for medical and recreational use of cannabis. In the process, however, marijuana has gone from reefer madness to ambrosia, in the minds of many people. Anecdotal reports of marijuana being able to cure anything from ADHD and Alzheimer’s to cancer abound on the internet. Medical studies that support such claims are a different matter, however. Because marijuana is still illegal at the federal level, scientists find it incredibly difficult to jump through all the regulatory hoops, including going past the DEA. There is only one accepted supplier that scientists can contact to access marijuana for research — the University of Mississippi, which runs the only legal marijuana farm, from a federal perspective. To make matters worse, the marijuana grown here is alleged of poor quality, according to some researchers. 

The point I’m trying to make is that marijuana is extremely understudied — at least not proportional to the staggering number of people who use it on a regular basis. As such, people should express caution and a balanced outlook. Research is luckily accelerating work that investigates cannabis’ health effects, but also those of other psychoactive substances like LSD, psilocybin or MDMA, which appear to have medical properties, particularly in treating addiction and mental disorders. It might take another decade before we can reach a consensus of how safe and in what kind of setting such substances can be used.