Does weed cause cancer?

Weed (marijuana smoke) has been shown to be carcinogenic. But does weed cause cancer? And if THC may help treat cancer, why the confusing messages? More on weed and cancer here.

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Marijuana smoke is carcinogenic. But does that mean that weed causes cancer? We explore here.

Marijuana and cancer: Cause and effect?

Before we begin to look at studies that tie marijuana use to cancer, we should first define a “causal relationship” as used by scientists in scientific studies. In a causal relationship, there is a cause and effect. In other words, one action (smoking weed) causes another (cancer). So as we review the causality between weed and cancer, we are actually talking about the relationship between SMOKED marijuana and the development of cancer.

Carcinogens: Marijuana smoke vs. tobacco smoke

Marijuana smoke and tobacco smoke are similar in both chemical composition and in toxicological properties. At least 33 individual constituents present in both marijuana smoke and tobacco smoke are already listed as carcinogens. But you might be surprised at the number of carcinogens in marijuana smoke. In fact, marijuana smoke contains 50-70% more carcinogenic hydrocarbons than tobacco smoke.

Marijuana smoking and types of cancer

In 2009, the State of California’s Environmental Protection Agency (EPA) placed smoked marijuana on a list of chemicals known to cause cancer. Among 19 categories of cancer reviewed for which rate ratio estimates were reported for direct marijuana smoking, statistically significant associations were reported in five categories. This means that the studies targeted marijuana smoking ONLY, not combined tobacco and marijuana smoking. The strongest evidence for a causal association between direct marijuana smoking and cancer comes from studies of head and neck cancer. The evidence is less strong but suggestive for lung cancer (Does weed cause lung cancer?), bladder cancer, and brain cancer and testicular cancer. So, the most common forms of cancer caused by marijuana smoking include:

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  1. bladder cancer
  2. brain cancer
  3. head and neck cancer
  4. lung cancer
  5. testicular cancer

Indirect marijuana smoking and cancer

Some causality exists between parental marijuana smoking and childhood cancer. Childhood cancers associated with maternal marijuana smoking are acute myeloid leukemia, neuroblastoma, and rhabdomyosarcoma. Childhood cancers associated with paternal marijuana smoking are leukemia (all types), infant leukemia (all types), acute lymphoblastic leukemia, acute myeloid leukemia, and rhabdomyosarcoma. However, studies that link cancer to second hand marijuana smoke are limited by potential biases and are small in numbers for most types of cancer. In other words, more research is needed in this area.

Can THC treat cancer?

Wait a minute. Weren’t we just talking about how marijuana is so bad for you? Well, yes. But the main active ingredient in marijuana (THC) can also be used for good. In fact, some people think, “Yes, THC can help cancer patients.” So why such different thinking?

Well, the basic science of cancer treatment and marijuana is that THC (which is taken in pill form and not smoked) can first help care for symptoms such as nausea, vomiting and pain for people diagnosed with cancer. THC has also been helpful in stimulating appetite in cancer treatments. But an additional possibility has been recently discovered: Cannabinoids as anticancer agents.

In other words, THC might actually slow the growth of tumors. How? THC has been shown in culture and animal studies to inhibit the genes that make a certain protein called vascular endothelial growth factor (VEGF), in effect, inhibiting the growth of tumor cells by modulating key cell signalling pathways. Because cannabinoids are usually well tolerated, and do not produce the same effects as chemotherapy, doctors and researchers are looking to THC as a new anticancer alternative.

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Weed and cancer questions

In sum, it seems that your medicine can also be your poison. While marijuana can be used a medicine for some medical conditions, when smoked to excess, pot can also trigger cases of  cancer.  If you have questions about the use of marijuana, THC and cancer … please ask them here. We try to answer all earnest questions personally and in good time. You can also send us an email. But feel free to comment about marijuana and cancer below.

Reference sources: Evidence of the caricinogenicity of Marijuana Smoke
Marijuana: Addiction Medicine Education Series Workbook from the State of New York
NIDA Marijuana: Facts Parents Need to Know
About the author
Lee Weber is a published author, medical writer, and woman in long-term recovery from addiction. Her latest book, The Definitive Guide to Addiction Interventions is set to reach university bookstores in early 2019.


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  1. This article was very informational. Although, these cancers don’t occurs often. I have heard that smoking weed has a relation to lower sperm cells. Does that apply only to smoking or simply consuming any form of THC?

    1. Hi George. Marijuana and THC have impact on lower sperm count no matter the mode of administration.

  2. My friends smoke weed and I’ve was around them a few times but also I would smell it on them. Does that affect me in any way??

  3. I believe that if marijuana needs to be used for what ever medical purpose, it should be used. I also understand that if that person chooses to take marijuana as treatment, their should be a way that the patient doesn’t become actively addicted. This drug has both pros and cons, but If the person isn’t allowed to use it then their should be something else they can take and will be just as affective, but way less harmful.

  4. Hi Jordan. I’d suggest that it’s best you go to a doctor and have it checked out. Bladder cancer has been linked to smoking, a parasitic infection, radiation and chemical exposure. But researcher haven’t connected marijuana use with the appearance of bladder cancer, and some studies even show that marijuana might decrease the risk for bladder cancer.

  5. I myself am not a smoker of marijuana but my friends are and I have been around them while they smoke only a couple of times. Just recently I have found a small bump near my bladder with redness on the skin. Could this be bladder cancer due to secondhand smoke from marijuana?

  6. I am trying to find out the variety names that marijuana has and what ones help for what pain?? I recently tried Pineapple express and calmed me down and Og kush took my pain away. If someone could answer my questions I would appreciate it.

  7. Hello Sandra. You can receive a prescription for THC pills from a medical doctor in a state that has legalized medical marijuana. To date, 19 states and jurisdictions have decriminalized or legalized marijuana for personal or medical use.

  8. I like the THC portion of the article, but CBD will often prevent cancer. Marijuana smokers have a FAR less chance of getting ANY cancer even though what you say is true. However, there is also the vaporizer option, which doesn’t burn the plant matter, just the THC and/or CBD/CBN. Giving them almost no chance of getting cancer.

    What you say about cigarettes in comparisson to marijuana is a bit ridiculous to point out without also pointing out that cigarettes have added cyanide and formaldehyde…etc. I think that “might” put cigarettes far above marijuana in terms of danger.

    I don’t mean to sound rude. I have studied the use of marijuana for 13 years in various ways. I appreciate the intent of this article, but it sure makes marijuana look FAR more dangerous than it is. Even in it’s worst form, smoked in paper, it is safer than many of the things we can find in our food at the grocery store. I call it a miracle plant. God put it here for more than just cancer too. Ie: Crohn’s,anxiety, depression, it can be some of the healthiest food when juiced and you wouldn’t even get high. Im sorry Im so passionate, but we take greater chances everyday with “regular” things and it is fully accepted.
    Our studies are needed for more important things. Did you know there are between 60 – 120 different kinds of cannabinoids at a different ratio in each of the thousands of strains? No two alike. Each strain has a job. Let’s focus on that first.

  9. I am sooo confused! I smoke marijuana out of a pipe once a week. Is this going to cause cancer? I keep reading online that it does and that it doesn’t. I wish I could know the absolute truth! Help!

  10. Hi Barney. Just to clarify. The cases of cancer listed above are not common, but they do occur. And it is much riskier to smoke weed than to ingest cannabis orally (either by pill OR in oils/resins while cooking).

    Does this help?

  11. Good article. I am not a pot smoker, but my son is and I was not aware that marijuana could cause so many different types of cancer. I did some research and could not find any studies that came to this conclusion. Only thing I could find was a UCLA study that concluded no marijuana did not cause cancer. Please reply as this is important to me.

    This copied website address is a link to a article referring to said study.

  12. Back here in India, I am trying to use this on my mother on whom doctors have clearly given up. Might as well go back to mother nature and allow it to decide rather than coughing up thousands of dollars for resultless, painful treatment.

  13. I’m a medical cannabis user. All of us need to check out and defend our rights, As well as try to legalize medical related Weed everywhere. That way it can end up being less complicated in order to get personal medication, without having to worry about legal requirements.

  14. I don’t know how a drug that provides both negative and positive effects can be illegal, whilst drugs like alcohol and tobacco, which only provide negative effects are legal.


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