Patients with colorectal cancer and a history of cannabis use disorder face a dramatically higher risk of death within five years compared to those without the disorder, according to a new study published in the Annals of Epidemiology. The study found a five-year mortality rate of 55.88% in patients with cannabis use disorder, compared to just 5.05% in those without it—indicating more than a 20-fold increase in risk (odds ratio [OR] = 24.40; 95% CI = 11.39–52.34; P < .001).
“This study adds to a growing body of evidence suggesting that heavy cannabis use may have underrecognized impacts on the immune system, mental health, and treatment behaviors—all of which could influence cancer outcomes,” said lead author Dr. Raphael Cuomo, Associate Professor of Anesthesiology at UC San Diego School of Medicine.
The researchers analyzed data from 1,088 patients in the University of California Health Data Warehouse who were diagnosed with primary colon cancer and had undergone drug use disorder screening prior to diagnosis. Of those, 34 had a history of cannabis use disorder.
Even after adjusting for key demographic and clinical factors, such as the cancer biomarker CEA, the risk remained significantly elevated. The adjusted odds ratio showed a tenfold increase in mortality risk (OR = 10.52; 95% CI = 5.76–19.22; P < .001). The hazard ratio, which measures risk over time, was reduced to 6.39 when factoring in demographics and clinical conditions (95% CI = 2.85–14.31; P < .001).
Dr. Cuomo noted that cannabis use disorder is frequently linked with mental health conditions like depression and anxiety, which may interfere with a patient’s ability to follow through with treatment. “This isn’t about vilifying cannabis,” he emphasized. “It’s about understanding the full range of its impacts, especially for people facing serious illnesses.”
The study underscores the need for further research into how chronic cannabis use affects cancer progression, treatment engagement, and survival. It also highlights the importance of nuanced, evidence-based discussions around cannabis use in oncology settings.
