Background: Pain is a common reason for patients with cancer to seek care in the Emergency Department (ED). Many of these patients are on chronic opioids and may have developed opioid tolerance, which makes appropriate dosing challenging for emergency physicians. Therefore, we designed an electronic medical record (EMR) based best practice advisory (BPA) intervention to recommend appropriate opioid dosing in the ED, based on a patient’s prescription opioid use. Methods: We conducted a retrospective cohort study to evaluate our cancer pain intervention at two academic EDs from May 2020 to May 2022. Our novel BPA algorithm identified ED cancer patients who were taking prescription opioids with an EMR-calculated morphine equivalent daily dose (MEDD) of at least 100. If an ED provider ordered an opioid for one of these patients, the BPA would fire and recommend an opioid dose based on the patient’s individual MEDD. The ED provider would then have the option of accepting or cancelling the BPA. We compared outcomes based on whether patients received BPA-guided increased opioid dosing. We utilized the chi-squared test with an alpha of < 0.05 to assess the relationship between BPA-guided increased opioid dosing and pain scores, hospital admission rates and ED bounce-back rates (return visit within 7 days). Results: We identified 399 patients who met our inclusion criteria, representing 705 BPA alerts. Those patients that received increased opioid dosing were similar to those that did not, with respect to age, sex, race/ethnicity and ECOG score. Patients who received BPA-guided increased opioid dosing experienced a greater improvement in pain (72.5% vs 65.1%, p = 0.03) and were admitted less frequently (58.5% vs 63.9%, p = 0.04). However, among discharged patients, those that received increased opioid dosing bounced back to the ED more frequently (16.2% vs 7.7%, p < .01). Conclusions: This EMR-based BPA intervention was associated with improved pain scores and decreased admission rates among cancer patients visiting the ED. The same intervention, however, was associated with increased ED return visits within 7 days, suggesting that pain management strategies may need to be implemented or modified upon ED discharge to assure that patients’ symptoms are adequately managed at home.