A groundbreaking study from the University of California San Diego (UCSD) has uncovered a concerning link between heavy cannabis use and increased mortality rates among colon cancer patients. The findings raise important questions about the long-term effects of cannabis use, particularly within medically vulnerable populations like those living with cancer.

Understanding the Study on Cannabis Use and Colon Cancer

Researchers at UCSD’s School of Medicine analysed medical records from over 1,000 colon cancer patients treated at University of California Health hospitals between 2012 and 2024. Their goal was to examine whether a history of high cannabis use impacted patients’ outcomes following their colon cancer diagnosis. Specifically, they assessed five-year mortality rates by comparing patients with a documented history of cannabis use disorder (CUD) to those without.

The results were revealing. Of those diagnosed with CUD, the five-year mortality rate reached a troubling 55.88%, compared to just 5.05% among patients without CUD. This means colon cancer patients with prior CUD were more than 24 times more likely to die within five years of their diagnosis.

What the Research Tells Us About Cannabis and Cancer

Dr Raphael Cuomo, lead researcher and associate professor in UCSD’s Department of Anesthesiology, explained the potential implications of the findings. “This study adds to a growing body of evidence suggesting that heavy cannabis use may have underrecognised impacts on the immune system, mental health, and treatment behaviours. All of these factors could influence cancer outcomes.”

The researchers note that some laboratory studies have shown anti-tumour effects of certain cannabis compounds. However, real-world cannabis use is far more complex. The team emphasised that while this research highlights risks specific to heavy cannabis use, it is not intended to vilify the drug entirely.

Dr Cuomo further elaborated, “High cannabis use is often associated with depression, anxiety, and other challenges that may compromise a patient’s ability to engage fully with cancer treatment. These findings are about understanding the full range of its impacts, particularly on populations facing serious illnesses.”

Why Heavy Cannabis Use May Increase Mortality

The study highlights several mechanisms that could explain this increased risk:

1. Immune System Disruption

Cannabis, especially when used heavily over time, has been shown to influence immune system functioning. While certain cannabis compounds may help reduce inflammation, chronic use could suppress the immune system’s ability to defend against illnesses, including cancer.

2. Mental Health Challenges

Mental health conditions like anxiety or depression are often linked to heavy cannabis use. Both can deter patients from fully engaging with treatment plans or maintaining the motivation needed to follow through with their care.

3. Adherence to Treatment Plans

Cannabis use disorder can make it difficult for patients to adhere to the demands of rigorous cancer treatment protocols, such as attending appointments, taking medications as prescribed, or making necessary lifestyle adjustments.

The surrounding lifestyle choices of heavy cannabis users might also play a role. Research suggests that smoking cannabis, for example, could have similar harmful effects on lung health as tobacco use, which might further complicate cancer recovery.

However, this study also highlights the need for more inquiry. “We hope these findings encourage more research and more nuanced conversations about how cannabis interacts with cancer biology and care,” Cuomo commented.

Cannabis Use Versus Cannabis Compounds

A point worth highlighting is the difference between the effects of pure cannabis compounds and cannabis use as a whole. While some studies have indicated anti-cancer properties associated with cannabinoids like THC or CBD, this study focused strictly on patients with a documented history of problematic, heavy cannabis use.

Real-world cannabis often contains variable levels of active compounds and contaminants like pesticides or mould that laboratory-controlled cannabinoids don’t. That’s why the researchers caution against equating selective cannabinoid studies with overall cannabis use. The findings underscore the importance of considering the wider, and often mixed, real-world impacts of the drug.

Why These Findings Matter

The growing social acceptance and legalisation of cannabis mean such findings carry significant weight. Cannabis use for medical and recreational purposes has surged in recent decades, but researchers still do not fully understand its long-term effects.

These results highlight that while cannabis may help with certain conditions, people should approach its use among vulnerable populations carefully. For colon cancer patients, especially, understanding how cannabis use may interact with the biology of their disease is critical. Healthcare providers and patients alike need clear, evidence-based guidance about the role cannabis might play—not just as a complementary therapy, but as a potential risk factor.

What Does This Mean for Patients and Healthcare Professionals

For patients with colon cancer, the study provides an opportunity to take an honest look at the role cannabis might play during and after their treatment. Open communication with their medical teams about their cannabis use should be encouraged. Notably, healthcare professionals might also consider screening for cannabis use during initial consultations to factor it into an individual’s treatment plan.

The researchers also hope this study prompts policymakers to consider ways to monitor and manage cannabis use among patients with chronic conditions. While the drug offers growing potential for therapeutic purposes, its use in medical treatment comes with complexities requiring more comprehensive research.

Towards More Research and Awareness

This study from UCSD has successfully put heavy cannabis use and colon cancer outcomes under the spotlight. But it also highlights the need for deeper investigation. Future research must explore whether the timing and amount of cannabis consumption play a role in these observed outcomes. Additionally, isolating specific cannabinoids in studies might reveal whether these compounds can treat cancer without their associated risks.

At its core, this research isn’t about labelling cannabis as “good” or “bad.” Instead, it’s about equipping both patients and healthcare providers with the full picture. Understanding cannabis use and its link to cancer mortality is vital for better patient care and informed decision-making.

Source: UC San Diego Today