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Marijuana comes from the cannabis plant. The main psychoactive ingredient in marijuana is THC (delta-9-tetrahydrocannabinol). THC is a type of cannabinoid. There are many other types of cannabinoids in marijuana. Cannabinoids are chemicals that act on certain receptors on cells in our body.

  • Marijuana and cancer

    It is biologically possible for smoking marijuana to increase cancer risk since marijuana smoke contains many of the same carcinogens as tobacco smoke. Also, people who smoke marijuana tend to inhale more smoke per puff and hold it in their lungs for longer than people who smoke tobacco cigarettes.

    We need more evidence to know for sure about the possible cancer risk. Some studies suggest that using marijuana over a long period of time may increase the risk of cancer, particularly cancers of the lung, head and neck. However, the quality of this research is not as strong as the evidence on tobacco and cancer. Other studies do not show an increased risk of cancer after long-term marijuana smoking.

    The fact that many people who smoke marijuana also smoke tobacco or mix the marijuana with tobacco makes it harder to know whether marijuana causes cancer. Also, because there is no standard amount of THC (the main active ingredient in marijuana) in every marijuana cigarette, it is hard to compare results across different studies.

  • Our perspective

    There are limits to the current evidence, but the Canadian Cancer Society is concerned that long-term marijuana smoking may raise your risk of cancer.

    Research on whether or not long-term smoking of marijuana is a risk factor for cancer is conflicting. We recommend that more research be conducted to better understand the cancer risks associated with long-term recreational smoking of marijuana and of exposure to second-hand marijuana smoke.

  • More information

    Health Canada provides information about marijuana including the short- and long-term health effects of using it.



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