Marijuana: Does it cause cancer?

Originally Published: March 23, 1995 - Last Updated / Reviewed On: March 11, 2014
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Dear Alice,

I have been reading some of your info about marijuana. My question is: If it is so much stronger than smoking cigarettes and has some of the same ingredients, why don't we hear reports of people who have some form of cancer?

Dear Reader,

Conclusions about long-term drug effects need long-term research studies, and that's why the jury is still out on some of the cannabis consequences that may show up down the road. Despite the fact that humans have been growing the marijuana plant for thousands of years, and using it recreationally in the U.S. since the early twentieth century, its effects have not been as thoroughly studied as those of tobacco and cigarette smoking.

From the studies which have been conducted, we know that incidents of cancer from cigarette smoking are far more numerous than cancers from smoking pot, at least in part because more people smoke cigarettes. Also, even frequent marijuana users tend to consume less than heavy cigarette smokers. One thing to keep in mind, though, is that marijuana smokers usually inhale more deeply and keep the smoke in their lungs for a longer period than tobacco smokers. It is possible that these behaviors increase the lung's exposure to the chemical by-products of smoking. Burning marijuana for smoking releases many substances other than THC, the ingredient which produces the drug's psychoactive effects. THC does not appear to be carcinogenic, but some of the other chemicals released by both marijuana and tobacco smoke are problematic. These include tar, carbon monoxide, and cyanide. One known carcinogen, benzopyrene, though found in both types of smoke, seems to be greater in pot smoke.

When it comes to health problems related to breathing and their lungs, heavy smokers of either substance have more difficulty than nonsmokers. These include chronic cough, phlegm, wheezing, and bronchitis. Some studies have indicated that people who smoke both marijuana and tobacco may be more likely to develop lung cancer, and at an earlier age, than smokers of tobacco alone.

There are some other things to think about. For one, pot is usually not smoked with a filter. Using one would cut down on the amount of "bad" chemicals entering the body. Some researchers also suggest that inhaling marijuana deep into the lungs and holding it there is something smokers should stop doing. Apparently, this ritualized practice does not significantly increase the drug's effect anyway.

For now, it does appear that pot smokers may run an increased risk of cancer, as well as bronchial irritation and possibly other health problems. However, there is not a consensus on this topic and there has not been enough investigation for the link to be clear.

Here are some resources with varying views and figures on marijuana-related issues — health effects, legalization, and the consequences of getting caught using and selling pot among them:

For more information about cancer, check out:

American Cancer Society (ACS)
National Cancer Institute (NCI)