Colon cancer patients with a history of cannabis use disorder may face a higher risk of death within five years of diagnosis, according to a new study.
Having cannabis use disorder (CUD) is linked to a tenfold increase in the odds of dying within five years after a colon cancer diagnosis, compared to those without the disorder.
The study did not measure the patients’ cannabis use in terms of dose or frequency.
“While cannabis may have therapeutic benefits for some conditions, real-world patterns of heavy use—particularly when associated with psychiatric or behavioral challenges—may carry serious risks for medically vulnerable patients,” study author Raphael E. Cuomo, a professor and biomedical scientist at the University of California, San Diego School of Medicine, told The Epoch Times.
Cannabis Use on Cancer Outcomes
Patients with a history of CUD had a five-year mortality rate of 55.88 percent, compared to just 5.05 percent for patients without such a history.
The study, recently published in the journal Annals of Epidemiology, analyzed electronic health records from more than 1,000 colon cancer patients treated across the University of California Health system between 2012 and 2024.
The research specifically examined how cancer outcomes varied based on patients’ history of cannabis use before diagnosis, accounting for factors including age, sex, and disease severity.
Cuomo, the sole author of the paper, theorizes that this may be due to how cannabis use effects the endocannabinoid system, a biological system in the body that helps regulate different physiological processes, including appetite, digestion, mood, and pain.
CUD is a clinical term for addiction to cannabis, characterized by continued use despite negative consequences, like health problems, social disruptions, or job difficulties, a condition that affected just 34 of 1,088 patients, or 3.1 percent, in the study.
Cannabis’s Effect on Treatment Through Immune System
The endocannabinoid system is known to affect inflammation and immune function, Cuomo said, and cannabinoids may impair anti-tumor activity by inhibiting T-cells and suppressing and altering immune responses. The endocannabinoid system is altered in many types of tumors.
High cannabis use has been associated with increased rates of depression and anxiety, both of which are independently known to affect treatment adherence and outcomes in cancer care, Dr. Yana Puckett, oncologist and medical director at the Survivorship Clinic and the High-Risk Breast Cancer Clinic at the Lewis Cancer Pavilion and Breast Cancer Expert at JustAnswer, told The Epoch Times.
“Patients experiencing mental health struggles may be less likely to attend appointments, adhere to complex treatment regimens, or report side effects early,” she added. “There may also be side effects that are more prevalent with cannabis use or more potent than without.”
However, Cuomo pointed out that available data did not include specific information about the types and formulations of cannabis that was used. He explained that the key variable he assessed in this study was whether the patient met the criterion of having cannabis use disorder.
“Future studies are needed to understand whether particular forms of cannabis use are more strongly associated with cancer outcomes,” Cuomo said.
Puckett emphasized that the findings highlight the importance of integrated care models that address both the physical and mental health needs of oncology patients, including screening for substance use and mental health conditions as part of routine cancer care.
Findings Surprise Experts
Although some research suggests certain compounds in cannabis could help fight tumors, the findings indicate that the real-world consequences of cannabis use may be more complex.
Christine L. Sardo Molmenti, a cancer epidemiologist at Northwell Health in New York who was not involved in the study, recounted how her department chair was absolutely surprised by the findings.
“We really hear about all the benefits of cannabis, and I think that’s why it’s been legalized in so many places,” Molmenti said. But information is currently missing on how it affects people with pre-existing health conditions, those with history of cancer, as well as other vulnerable populations at risk of potential adverse effects.
“I don’t think that’s out there yet,” Molmenti said.
She called for better screening tools for health care providers to accurately categorize problematic versus casual cannabis users, noting that the current study might include some misclassification due to inadequate assessment tools.
Dr. Sean Devlin, an integrative oncologist at Gerber Medical Clinic in Reno, Nevada, told The Epoch Times that cannabis use and cancer has been a “hot topic of debate” for some time, with growing access and legalization across the United States.
“This disorder [CUD] does not exist in a vacuum and may be accompanied by numerous other comorbidities,” Devlin explained. “CUD is often associated with depression, anxiety, and cognitive impairment, all of which can compromise adherence to cancer therapies and diminish treatment efficacy.”
As cannabis use becomes more socially accepted and widely used, researchers stress the importance of further exploring the drug’s long-term effects, particularly for those facing significant health challenges.
Cuomo said that “the key message is not that cannabis should be categorically avoided, but that an evidence-based understanding of its impacts in complex illnesses like cancer is urgently needed.”