Colon cancer is one of the most common cancers in the world and a major cause of death. Doctors have made progress in early detection and treatment, which has helped many patients live longer.
However, survival still depends on many factors, including age, overall health, stage of the disease, and how well patients follow treatment plans. A new study from researchers at the University of California San Diego School of Medicine suggests that another factor may also play an important role: heavy cannabis use before diagnosis.
Cannabis, also known as marijuana, has become more widely used in recent years as laws have changed and public attitudes have shifted. Some people use it for relaxation, while others use it to help with pain, anxiety, or sleep problems.
There has also been interest in whether certain chemicals in cannabis might help treat cancer symptoms. Because of this, many patients believe cannabis is harmless or even helpful during illness. However, scientists are still studying its long-term effects on serious diseases like cancer.
In this study, researchers examined medical records from more than 1,000 people treated for colon cancer within the University of California Health system between 2012 and 2024. They looked for patients who had a documented history of cannabis use disorder, which means frequent and heavy use that affects daily life.
The team then compared survival outcomes between these patients and those who did not have such a history, while also considering age, sex, and how advanced the cancer was at diagnosis.
The findings were striking. Patients with a history of heavy cannabis use had a much higher risk of dying within five years of being diagnosed with colon cancer.
More than half of these patients died during that period, compared to a small percentage of those who did not have a history of heavy use. After adjusting for other factors, the researchers found that patients with cannabis use disorder were more than 20 times more likely to die within five years.
Scientists believe several reasons may explain this difference. Heavy cannabis use has been linked to depression, anxiety, and other mental health challenges, which can make it harder for patients to attend appointments, follow treatment instructions, or maintain healthy habits.
Cannabis may also affect the immune system, which plays a key role in fighting cancer and responding to treatments such as chemotherapy. In addition, heavy use may be associated with lifestyle factors like poor sleep, unhealthy diet, or smoking, all of which can influence recovery.
It is important to note that some laboratory studies have suggested certain compounds in cannabis might slow cancer cell growth under controlled conditions. However, real-life use is far more complex. People use different products, doses, and methods of consumption, and these differences can lead to unpredictable effects.
The researchers emphasized that their findings do not mean cannabis directly causes worse outcomes, but they highlight a strong association that needs further investigation.
This study is important because cannabis use is increasing, especially in places where it has been legalized. Many cancer patients may assume it is safe without discussing it with their doctors.
The findings suggest that open communication between patients and healthcare providers is essential. Doctors may need to consider cannabis use when planning treatment and offer additional support to patients who struggle with heavy use.
From a scientific perspective, the results raise important questions about how cannabis interacts with cancer biology and patient behavior. The study relied on medical records, which means it could not capture every detail about how much cannabis was used or how it was consumed.
More research is needed to confirm the findings and to understand whether reducing heavy use could improve survival. Future studies may also explore whether certain groups of patients are more vulnerable than others.
Overall, the research suggests that heavy cannabis use may be an overlooked factor in cancer care. While cannabis may help some people manage symptoms, excessive use could interfere with treatment and recovery.
Patients facing serious illness should talk openly with their healthcare team about all substances they use so they can receive the safest and most effective care possible. Understanding these risks can lead to better decisions and potentially better outcomes for people living with colon cancer.
If you care about cannabis, please read studies that what you need to know about cannabis and heart attack, and CBD from cannabis may help inhibit COVID-19 infection.
For more information about cannabis, please see recent studies that medical cannabis could help reduce depression, and results showing this stuff in cannabis may protect aging brain, treat Alzheimer’s.
The study is published in Annals of Epidemiology.
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