Pot Smoke: Less Carcinogenic Than Tobacco?

Researchers Say THC May Curb Cancer-Causing Effects of Marijuana Smoke

Medically Reviewed by Louise Chang, MD on October 17, 2005
From the WebMD Archives

Oct. 17, 2005 -- Although tobacco smoke and marijuana smoke are chemically very similar, a new report argues that their cancer-causing effects may be very different.

Both tobacco and cannabis smoke contain the same cancer-causing compounds (carcinogens). Depending on what part of the plant is smoked, marijuana can contain more of these harmful ingredients.

But a recent review of studies on the effects of marijuana and tobacco smoke suggests that the cancer-promoting effects of these ingredients is increased by the tobacco in nicotine and reduced by the tetrahydrocannabinol (THC) found in cannabis.

Previous studies have shown that THC can inhibit carcinogens in mice, and the report suggests it may have the same protective effect against the carcinogens found in smoke in humans. But researchers warn that even if THC lessens the effects of these cancer-causing ingredients, cannabis smoke remains carcinogenic.

The Role of THC

In the article, published in Harm Reduction Journal, researcher Robert Melamede, PhD, of the University of Colorado at Colorado Springs, argues that tobacco smoke and marijuana smoke are not equally cancer-causing.

Research shows that nicotine and THC act on related pathways in the body, but they bind to different receptors to activate these pathways. For example, Melamede says the cells of the lungs are lined with nicotine receptors but do not appear to contain receptors for THC.

He says that may explain why marijuana use has not been linked to lung cancer as cigarette smoking has.

However, Melamede says the effects of cannabis and cannabis-like compounds are complex and sometimes contradictory. The long-term effects of marijuana on an aging population of users are not known; the effects may become similar to what we see with tobacco. Also, marijuana is frequently used in combination with tobacco and the two drugs may interact in yet unknown ways.

Show Sources

SOURCES: Melamede, R.Harm Reduction Journal, Sept. 22, 2005; vol 2. News release, BioMed Central.
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