When Cannabis Hurts: Colon Cancer Mortality Linked to Overuse

A Closer Look at Cannabis and Cancer Survival

As conversations around cannabis continue to evolve, more attention is being paid to how it impacts not just general wellness, but serious illnesses like cancer.  While many studies point to potential benefits of cannabis for cancer patients — from easing pain to enhancing quality of life — a new study¹ out of the University of California, San Diego, paints a more cautionary picture when it comes to cannabis use disorder (CUD) and colon cancer survival.

The relationship between cannabis and cancer is complex.  It is not as simple as “good” or “bad.”  Rather, a deeper understanding of how cannabis use — and misuse — is required, which might biologically and behaviorally influence outcomes for vulnerable patients.

Study Findings: Cannabis Use Disorder and Higher Mortality Risk

To generate its insights, the study, published in Annals of Epidemiology, analyzed medical records from 1,088 patients diagnosed with primary colon cancer.  The researchers behind the work specifically focused on individuals who had undergone drug use disorder screenings before their cancer diagnosis.  Of those screened, 34 patients were found to have had a documented pre-existing diagnosis of cannabis use disorder.  Their key findings included:

• Patients with CUD had a five-year mortality rate of 55.9%, compared to 5.1% for patients without CUD.
• After adjusting for age, gender, and disease severity, patients with CUD were over 10 times more likely to die within five years.
• When alternative markers of cancer stage were used, the association between CUD and mortality remained significantly elevated.

These results strongly suggest that a history of cannabis use disorder is an independent risk factor for worse outcomes in colon cancer patients.

A Possible Biological Explanation

While the findings may indicate that CUD may present a significant risk factor for colon cancer patients, the ‘why’ remains in question.  From a biological standpoint, it is thought that cannabis may impact the immune system in ways that make it harder for the body to fight off cancer.  One mechanism supporting this involves the suppression of T-cell activity, which plays a critical role in recognizing and destroying cancer cells.  When T-cells are inhibited, the body’s ability to detect and eliminate malignancies may be weakened.

Then there is the fact that cannabis can also disrupt cytokine signaling, a process that helps coordinate immune responses.  Alterations in cytokine production can affect how the immune system responds to developing tumors, potentially allowing cancers to progress more easily.  Another factor is the inhibition of antigen presentation.  By impairing the immune system’s ability to identify cancer cells, cannabis use may reduce the chances of mounting an effective anti-tumor defense.

Simply put, through its effects on the immune system, CUD may not only decrease the body’s ability to detect cancer cells, but also its ability to appropriately respond and destroy them.

Opposing Viewpoints: The Case for Cannabis Benefits in Cancer Care

While this study draws much-needed attention to the potential dangers of cannabis use disorder, it is equally important to recognize that not all cannabis use is problematic — and for many cancer patients, cannabis has become a key part of their care plans.

For example, a recent meta-analysis highlighting this looked at over 3,000 cancer patients and found that medical cannabis provided strong, sustained relief across a variety of symptoms. Patients reported significant improvements in:

• Pain
• Sleep quality
• Emotional distress
• Appetite stimulation

Moreover, the meta-analysis found that many participants reduced their reliance on traditional medications, including opioids and antidepressants, after starting medical cannabis therapy — an important consideration in light of the ongoing opioid crisis.

Similarly, a 12-month QUEST Initiative discovered that medically supervised cannabis use could lead to long-term improvements in anxiety, chronic pain, insomnia, and overall quality of life for cancer patients.

What sets therapeutic cannabis use apart from CUD is intent, medical supervision, and responsible use.  Therapeutic cannabis is often carefully titrated and monitored by healthcare providers, aiming for symptom relief without impairment or addiction.  This distinction is crucial — and often overlooked — in public discussions about cannabis and health.

Limitations of the Study: What Readers Should Know

As with all research, it is essential to acknowledge the limitations of this study.  The reliance on electronic health records to diagnose cannabis use disorder could lead to some misclassification. For instance, patients who were using cannabis therapeutically might have been incorrectly labeled as having a disorder.

Furthermore, the study could not track whether patients changed their cannabis use patterns after receiving a cancer diagnosis, leaving room for potential reverse causation.

Finally, this study was observational.  While it may have demonstrated a strong association between cannabis use disorder and mortality, it does not prove that CUD directly causes higher mortality rates.

The Bigger Picture: Tailoring Cannabis Conversations for Cancer Patients

This research serves as an important reminder: cannabis is not risk-free, particularly when used in ways that lead to dependence or problematic behavior.  However, responsible, medically supervised cannabis use can offer profound benefits for cancer patients, improving daily living and reducing reliance on riskier pharmaceuticals.

As cannabis becomes more accessible, the need for thoughtful, individualized approaches to its use becomes even more critical.  These new findings offer evidence that cannabis use disorder can significantly worsen colon cancer outcomes, but they also reaffirm the real and powerful benefits cannabis can provide when used appropriately.

Overall, the message is clear: cannabis has great potential — but intent, supervision, and balance are key.  A deeper, evidence-based understanding of cannabis’s role in cancer care is not just helpful — it is essential for improving patient lives.

Studies Referenced:

^{1. Cuomo, R. E. (2025). Cannabis use disorder and mortality among patients with colon cancer. Annals of Epidemiology, 106, 8–10. https://doi.org/10.1016/j.annepidem.2025.04.012}