Objective: The purpose of this study was to evaluate the efficacy of subcutaneous morphine for managing pain crises resulting from various causes in cancer patients attended by the Pain Clinic in the immediate care area of the National Cancer Institute in Mexico City.
 Materials and Methods: This study was analytical, observational, retrospective, and descriptive. The oncology patients treated in the immediate care area for pain crises between August 1, 2020, and July 1, 2023, made up our study population. We documented the management of pain crises for patients who needed subcutaneous morphine treatment.
 Results: Considering a reduction in Numeric Rating Scale (NRS) score >30% as effective and a reduction <30% as ineffective, 566 patients didn’t require an additional dose of subcutaneous morphine to control the pain crisis; 11 patients reported a decrease of <30%. A total of 24 patients needed a second rescue. Among this group, only 5 responded well to the second morphine rescue; in the remaining 19 patients, the rescue was deemed ineffective if the NRS decreased by at least 30%. Only 5 individuals experienced moderate pain, and only one patient reported severe pain. The variables were compared using the non-parametric Mann-Whitney U test with significance <0.05. Consequently, it may be said that there is a statistically significant difference between the first and subsequent NRS values obtained.
 Conclusion: For oncology patients treated by the Pain Clinic in the immediate care section of the National Cancer Institute in Mexico City, subcutaneous morphine is beneficial in managing pain crises of different origins.
 Keywords: Morphine, Subcutaneous Pain crises, Efficacy, Numeric rating scale