Opioids play an important role in the management of moderate-to-severe pain; however, no universally accepted conversion standard is available across different opioids, formulations, and routes of administration, and conversion factors vary among clinical guidelines, expert consensus statements, and professional reference tools. This narrative review with descriptive evidence synthesis, focusing on the clinical application of opioid dose conversion, integrates recommendations from domestic and international guidelines, expert consensus statements, professional organizations, institutional clinical algorithms, pharmaceutical databases, and specialty conversion tools. Oral morphine equivalent (OME) conversion factors for commonly used oral, parenteral, and special opioid formulations were compared and descriptively summarized, and specific conversion scenarios such as transdermal fentanyl, methadone, buprenorphine, intrathecal administration, and other complex conversion scenarios. The findings show that conversion factors from different sources are relatively consistent for some opioids, whereas substantial variation remains for certain drugs and routes of administration. Fixed linear conversion is particularly inappropriate when dose-dependent, formulation-specific, or nonlinear conversion strategies are required. Opioid equivalence calculations should be used primarily for initial dose estimation. In clinical practice, incomplete cross-tolerance, previous opioid exposure, reasons for switching, organ function, concomitant medications, and individual risk factors should be considered, followed by timely reassessment and dose titration. By comparing conversion recommendations across multiple evidence sources and their scope of application, this review provides a practical reference for standardized and individualized opioid conversion in clinical practice.

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