A new study conducted by the University of California San Diego School of Medicine has revealed a concerning association between high cannabis consumption and a significant increase in five-year mortality among colon cancer patients. This research raises urgent questions about the effects of cannabis on medically vulnerable populations, amid its growing social acceptance and legalization.

An Unexpected Link Between Cannabis and Mortality in Colon Cancer

Over the past decades, medicinal and recreational use has surged in the United States and other countries. However, the long-term effects of cannabis consumption in patients with severe illnesses remain poorly understood.

Based on electronic medical records of over 1,000 patients treated between 2012 and 2024 within the University of California’s healthcare system, the study led by Dr. Raphael Cuomo found that patients with a history of cannabis use disorder (CUD) were 24.4 times more likely to die within five years of their colon cancer diagnosis compared to those without such a history.

Numerically, the five-year mortality rate for patients with excessive cannabis use history was an alarming 55.88%, compared to only 5.05% among those without CUD. Researchers controlled key variables such as age, gender, tumor stage, and specific cancer biomarkers, reinforcing the validity of the correlation found between cannabis consumption and adverse clinical outcomes.

Cuomo, an associate professor in UC San Diego’s Department of Anesthesiology and a member of the Moore Cancer Center, emphasized that these findings are not meant to demonize the plant but rather highlight the urgent need to understand its multiple effects.

“This study adds to a growing body of evidence suggesting that excessive cannabis use may have unrecognized effects on the immune system, mental health, and treatment behaviors—all of which could influence cancer outcomes.”

A Complex Substance with Uncertain Effects in Severe Medical Contexts

While several laboratory studies have suggested that certain cannabis compounds, such as cannabinoids, might have antitumor properties, the clinical reality is far from simple. In medical practice, usage is influenced by multiple factors—from dosage and administration method to the patient’s psychological context—making it difficult to assess its impact uniformly.

One issue identified by researchers is that heavy cannabis use often coincides with mental health disorders such as anxiety or depression, which in turn may reduce adherence to cancer treatment. Lack of motivation, mental fatigue, or distrust in medical therapies could compromise the patient’s active participation in their recovery process. Furthermore, intensive cannabis use could alter immune system responses in individuals already weakened by cancer.

The increasing legalization of cannabis has promoted its perception as a harmless or even beneficial substance, which may create false expectations among patients facing serious diagnoses. However, this study suggests that, in certain cases, cannabis could have counterproductive effects, especially when used habitually and without medical supervision.

Call for Caution and Further Research

The study’s authors explicitly call for continued research into how cannabis interacts with different types of cancer and treatments. They insist that this is not about rejecting its use entirely but rather establishing clearer clinical criteria, backed by evidence, for its administration in patients with severe illnesses. This is especially relevant as access to cannabis becomes more normalized, often without proper medical guidance.

“We hope these findings encourage further research and more nuanced discussions on how cannabis interacts with cancer biology and treatment,” Cuomo stated.

Ultimately, the study suggests that cannabis, like any other substance with potential therapeutic and adverse effects, should be approached with scientific rigor rather than solely through social or cultural enthusiasm.

The new study from the University of California San Diego warns of a possible link between excessive cannabis use and increased mortality risk in colon cancer patients. While the medicinal potential of cannabis is not in question, these findings highlight the importance of a more cautious, evidence-based approach to its use in clinical settings. In the face of cancer’s progression and treatment challenges, every factor—including cannabis consumption—must be carefully evaluated.

Reference:

• Annals of Epidemiology/Cannabis use disorder and mortality among patients with colon cancer. Link

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