Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

“There are at least 33 carcinogens in marijuana smoke,” such as polycyclic aromatic hydrocarbons, which are products of combustion found in grilled meat and flowing through the bodies of those that smoke marijuana, similar to what one sees flowing through the bodies of cigarette smokers. That’s really remarkable: most tobacco users inhale way “more smoke into their lungs” over the course of a day, so on a puff-by-puff basis, is marijuana smoke really that much worse?

Well, it does seem to contain more benzopyrene and benzanthracene, which are “polycyclic aromatic hydrocarbon procarcinogens,” compared to unfiltered cigarette smoke. But it may just be that cannabis users inhale more deeply, and then hold the smoke in longer, which can end up depositing four times more tar in the lungs, “amplifying exposure” to these carcinogens. And, unfortunately, bubbling the smoke through water, like in a bong, does not appear to reduce the risks of tar buildup.

Yeah, marijuana smoke tar may have similar tumor-promoting effects as cigarette smoke… in mice, but what about in men (and women)?.

Longtime marijuana users do have more cancer, more lung cancer, more oral cancer, voice box cancer—but only, it seems, because they also tend to be more likely to also smoke tobacco. After cigarettes were taken out of the equation, no increased risk was found.

Same with head and neck cancer. One study found “increased risk,” but “five studies reported no association,” and “one study [found] decreased risk.” So yeah, “[r]egular use…causes airway injury [that can lead to] chronic bronchitis,” but no evidence of long-term lung damage, like emphysema. And, “[d]espite the presence of carcinogenic components,” no apparent increased risk of lung cancer— though “evidence is mixed regarding the risk of heavy, long-term use.” And that may be the crux.

In terms of smoke exposure, even smoking a joint every day for 10 years may only translate to six months of pack-a-day cigarette smoking. “In most studies on tobacco smoking and lung cancer,” six months in a lifetime might get you “classified as [a] never smoker.” It may take a couple years of cigarette smoking to significantly bump lung cancer risk; and so, that would be like smoking a joint every day of your adult life. No wonder we can’t find a lung cancer link with casual marijuana use, though there is an alternative explanation. Maybe the antitumor effects of the cannabis plant are counteracting “the tumor-promoting effects of the carcinogens…in the smoke.” Wait; antitumor effects?

Yes, in fact, the original demonstration of an anticancer effect, dating back to 1975, was against lung cancer cells, showing that THC can suppress their growth in a petri dish. This kind of data has led to wild claims of cancer cures “on the Internet, extrapolating the results of [this] preclinical work,” meaning like in petri dishes and test tubes, “to humans without any basis in fact,” as cannabis, according to this 2016 review, has not been studied clinically as a treatment for malignancy in people. But that’s not really true. There was a pilot study performed on terminal brain cancer patients. We’ll find out what they found, next.

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