Marijuana Smoke Is Carcinogenic ‒ Why Didn’t You Know That?

By | April 13, 2017 | 0 Comments


The title of this column is a rhetorical question. It is entirely clear why the vast majority of Americans ‒ and others ‒ do not know that marijuana smoke contains many of the same cancer-causing chemicals found in tobacco smoke. They were never told this important fact by the sponsors of legalizing medical marijuana, and then ‒ in a predictable step ‒ legalizing recreational marijuana.

What is worse, people were never told this fact by the mainstream media, which favor legalization of marijuana. And what is still worse, readers of some prestigious medical journals never saw this fact in print. Why not? The only reason I can think of is that the editors of these journals are so strongly in favor of legalizing recreational marijuana that they hesitate to allow authors to mention the carcinogens in its smoke.

To illustrate my point, here is a letter to the editor of the New England Journal of Medicine ‒ which, of course, was rejected:

The Perspective regarding recreational cannabis (Feb. 23 issue) (1) does not mention the fact that marijuana smoke contains many of the same carcinogens as tobacco smoke. Heavy marijuana smoking is associated with a twofold increase in the incidence of lung cancer, even after statistical adjustment for tobacco use, alcohol use, respiratory conditions, and socioeconomic status (2). Curbing tobacco use while legalizing marijuana is, in effect, replacing a carcinogen that increases alertness with a carcinogen that causes sedation. In view of the almost universal use of motor vehicles, does this make sense?

David C. Stolinsky, M.D.
Los Angeles, CA

1. Kilmer B. Recreational cannabis – minimizing the health risks from legalization. N Engl J Med 2017;376:705-7.

2. Callaghan RC, Allebeck P, Sidorchuk A. Marijuana use and the risk of lung cancer: a 40-year cohort study. Cancer Causes Control 2013;24:1811-20.

And here is a letter on the same subject to the Los Angeles Times ‒ which, of course, was also rejected:

Re “Health effects of pot are hazy,” California, Jan. 13

Perhaps the time to examine the health effects of marijuana was before its recreational use was legalized, not after. Still, in 33 column inches, the author finds no space to mention the word “carcinogens.” Even a cursory search of the Internet reveals that pot smoke contains most of the carcinogens of tobacco smoke. Why is this fact almost never mentioned in articles about pot? Why does Prop. 65 require warnings to be posted on gas pumps, as well as where balsamic vinegar and some types of fish are sold, but not at pot dispensaries? I’ll bet that not one percent of the voters who legalized pot knew about the carcinogens. Talk about an informed electorate!

David C. Stolinsky, M.D.
Los Angeles

Burning any plant matter ‒ wood, grass, leaves, tobacco, and the like ‒ produces polycyclic hydrocarbons, which are carcinogenic. People interested in reducing air pollution know this. So it is hardly surprising that burning marijuana leaves and stems produce similar carcinogens. What is surprising ‒ in fact, depressing ‒ is that other people try to suppress knowledge of this fact.

This reluctance to publicize the presence of carcinogens in marijuana smoke is but one example of how the media ‒ and even scientific journals ‒ distort the facts to favor their political agenda. But this is nothing new. Recall the aphorism of Sir William Osler, the most prominent physician of 100 years ago:

Believe nothing that you see in the newspapers…If you see anything in them that you know is true, begin to doubt it at once.

Osler would merely nod his head if he could know about the biased reporting in our “news” media. But he would be dismayed if he could see what is published ‒ and what is not published ‒ in our “scientific” journals. Bias is like mold. It creeps in where there is no sunlight and things are dark and damp. It grows unless measures are taken to control it. And like mold, bias can be toxic. It can be dangerous to our health ‒ both our political health and our physical health.

Author’s Note:
Subsequent to publication of this column, a study appeared on the health effects of second-hand marijuana smoke. In addition to containing carcinogens, second-hand marijuana smoke causes blood vessels to constrict. Tobacco smoke does the same, but marijuana smoke does it for a longer time. In short, besides the potential to cause cancer, we now must consider the possibility that marijuana smoke may cause vascular disease. Have a nice day.

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