Objective: Morphine is a common opioid used for managing pain in cancer patients, but its effects on survival, death, and cancer recurrence are unclear. While its pain-relieving properties are well-known, concerns about its impact on tumor progression and overall prognosis remain unresolved. This systematic review and meta-analysis aimed to assess the influence of morphine on these critical cancer-related outcomes.

Patients and Methods: A systematic review was conducted following PRISMA guidelines. Databases, including PubMed, Scopus, Web of Science, and Google Scholar, were searched for studies published until August 18, 2024, that evaluated the effects of morphine on survival, death, and recurrence in cancer patients. Data were extracted from 33 studies involving 373,882 cancer patients. Statistical analyses were performed using STATA, including subgroup analyses and meta-regression to assess the impact of morphine dose, route of administration, and follow-up periods on outcomes.

Results: Higher doses of morphine were linked to lower survival rates, with very high doses showing a 13% decrease in survival (95% CI: 3-24%). In contrast, intravenous administration was associated with higher survival rates (47%, 95% CI: 40-54%). High oral doses significantly increased mortality risk (HR = 16.09, 95% CI: 6.29-25.89), while recurrence was most frequent with moderate doses (46%, 95% CI: 38-54%) and intravenous morphine (38%, 95% CI: 33-42%).

Conclusions: Morphine’s impact on cancer outcomes varies with dose and route of administration. Higher doses, especially oral, are linked to worse survival and increased mortality. Clinicians should balance morphine’s analgesic benefits with these potential risks. Further research is necessary to refine opioid use in cancer care.