What We Know About Cannabis and Colon Cancer 

Cannabis and cancer have a long and complicated relationship. For some cancer patients, access to cannabis provides relief from treatment side effects like nausea and vomiting. Cannabis use may increase the risk of developing certain cancers. We currently have mixed findings about the relationship between smoking cannabis and lung cancer, with no conclusive evidence pointing directly at the plant as a cause for cancer.

But a new study recently emerged suggesting that cannabis use is associated with a higher colon cancer mortality rate. This naturally has turned some heads, especially since previous research had hinted at the potential for cannabis to prevent the development of colon cancer in mice.

So what does this new study mean? Here’s what we know about cannabis and colon cancer.

The Recent Colon Cancer and Cannabis Study

The University of California, San Diego School of Medicine recently published a study in the Annals of Epidemiology titled “Cannabis use disorder and mortality among patients with colon cancer.” In the study, researchers indicate that they have found a correlation between high cannabis use and colon cancer mortality.

The research shows that people with colon cancer and a documented history of heavy cannabis use were more than 20 times more likely to die within five years of their diagnosis than those without a history of heavy use.

To reach these findings, researchers used electronic health records from more than 1,000 colon cancer patients in the University of California Health system. The records spanned from 2012 to 2024.

The researchers looked at different cancer outcomes among patients with documented cannabis use before their diagnosis. The study’s controls included age, sex, and indicators of disease severity.

Here’s what they concluded:

• Patients with a documented history of cannabis use disorder (CUD) had a much higher five-year mortality rate than those without CUD: a 55.8% mortality rate vs. 5.05%.

• Those diagnosed with CUD before their cancer diagnosis were 24.4 times more likely to die within the first five years of their diagnosis compared to those without CUD.

These figures may be shocking at first glance. But let’s take a closer look at what this study tells us.

Important Considerations

Studies like these can be nerve-racking. But they’re important for us all to have a better understanding of the plant and its risks and benefits. Keep in mind that this study does not paint the whole picture.

Patients who use cannabis heavily often experience depression, anxiety, and other challenges that can interfere with their full engagement in cancer treatment, according to lead author Raphael Cuomo, Ph.D. “However, this isn’t about vilifying cannabis. It’s about understanding the full range of its impacts, especially for people facing serious illnesses. We hope these findings encourage more research — and more nuanced conversations — about how cannabis interacts with cancer biology and care,” said Cuomo.

In one review of the study, gastroenterologist Dr. Veeral Oza said that the study has some flaws. For example, Dr. Oza pointed out that the study was retrospective, meaning it can only point out the connection between cancer and cannabis use—and cannot link one as the cause of the other.

The study also doesn’t capture disease severity well and is missing over 40% of patient staging criteria. Once the data is adjusted for the limited amount of available severity data they had, the CUD effects are greatly reduced to between 5 and 7 times the odds and are only “marginally significant” with staging criteria considered. This effect is significant because it shows that many patients with severe disease are just more likely to reach for more cannabis anyway.

The study also appears to lack any controls for consumption methods. It’s unclear if the analyzed patients were regular smokers or if they were eating edibles or consuming cannabis in harmful ways, like smoking. This is likely the biggest study flaw and undermining feature.

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Smoking is a known contributing risk factor for all cancers, and burning cannabis can produce similar tar, free radicals, and carcinogens. This is an important factor that is entirely missed here, as smoking is still the most common method of cannabis consumption.

The study also doesn’t appear to go deep into what cannabis use disorder entails, or if habits changed after diagnosis, so it’s unclear just how much cannabis these subjects regularly consumed.

READ: Cannabis For Gut Health: How Cannabinoids Can Help with Gut Microbiome, ECS, and Digestive Disorders

Cannabis Use Disorder

The recent study points to patients with documented cannabis use disorder. According to the Diagnostic and Statistical Manual of Mental Disorders, DSM–5, cannabis use disorder is defined as “the presence of clinically significant impairment or distress in 12 months, manifested by at least 2 of the following:

• Cannabis is taken in larger amounts or used over a longer period than intended

• Persistent desire to cut down with unsuccessful attempts

• Excessive time spent acquiring cannabis, using cannabis, or recovering from its effects

• Cravings for cannabis use

• Recurrent use resulting in neglect of social obligations

• Continued use despite social or interpersonal problems

• Important social, occupational, or recreational activities are foregone to be able to use cannabis

• Continued use despite physical harm

• Continued use despite physical or psychological problems associated with cannabis use

• Tolerance

• Withdrawal symptoms when not using cannabis”

As evidenced by this list of diagnostic factors, cannabis use disorder is a broad term. It’s not clear which symptoms the patients with documented cannabis use disorder experienced, which makes it difficult to assess the exact role cannabis use plays in colon cancer mortality rates.

What We Do and Don’t Know About Cannabis and Colon Cancer

These types of studies can raise alarms among cannabis users and healthcare professionals. It’s good to be aware of what the recent science indicates, but it’s also important to know that we’re still learning every day, and it’s likely that new research will emerge in the future to provide more context about the relationship between colon cancer and cannabis use – especially if smoked.

For now, we know that some cancer patients choose to use cannabis for symptom management related to treatment and the cancer itself. Some patients may turn to cannabis to improve their nausea from chemotherapy or to reduce stress and anxiety related to their diagnosis, among other reasons. Avoiding cannabis smoking in favor of non-inhalational routes is a generally healthy rule of thumb and a great start.

A previous study showed promise for using cannabis to prevent colon cancer development, though the research was conducted on mice, not humans. Given that more recent science suggests that cannabis use is correlated with higher mortality rates in colon cancer patients, it’s clear that we need more comprehensive studies to gather a clearer picture.

For now, discuss the findings with your doctor if you are concerned about your cannabis use and its role in other medical conditions. For the prevention of colon cancer, ask your physician when to begin routine screening, pay attention to any unusual symptoms in your body, and follow the CDC’s recommendations for colon cancer prevention. Recommendations include staying active, maintaining a healthy weight, eating a low-animal fat, high fiber (fruits, vegetables, grains) diet, and limiting alcohol and tobacco use.