Opioids and immunosuppression in patients with cancer

Opioids remain the cornerstone of cancer pain management, yet a substantial preclinical literature suggests that opioids, particularly morphine, are immunosuppressive, raising concern about tumour surveillance, infection risk, and interference with immune checkpoint inhibitors (ICIs). This critical narrative review evaluates whether this preclinical signal is supported by clinical evidence sufficient to justify a change in practice. We show that the mechanistic case, mu-opioid receptor-mediated suppression of NK cell and CD8 + T-cell function, cytokine dysregulation, and central sympathoadrenal effects, is coherent and reproducible in vitro and in animal models. Clinical evidence, however, is limited to retrospective cohorts affected by confounding by indication: patients requiring opioids have more advanced disease, worse performance status, and greater systemic inflammation, all of which independently predict worse outcomes. We further highlight a largely neglected counter-argument: uncontrolled cancer pain is itself a potent immunosuppressant via HPA-axis and sympathoadrenal activation, and independently predicts shorter survival, so that inferior outcomes in opioid users may reflect the disease burden that necessitated opioid therapy rather than a pharmacological effect of the drug itself. We conclude that current evidence does not justify withholding or limiting opioid analgesia in cancer patients, including those receiving ICIs, and that prospective studies with pain-matched comparators are needed before any change in clinical practice can be recommended.