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:

  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.

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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