Opioid Conversion Calculator
Convert between opioid doses using equianalgesic ratios. Calculates morphine milligram equivalents (MME) with CDC risk thresholds.
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⚠️ Important: Always reduce calculated dose by 25–50% for incomplete cross-tolerance when rotating opioids.
Disclaimer: For educational purposes only. Not a substitute for clinical judgment.
About This Tool
What Is Opioid Equianalgesic Conversion?
Opioid equianalgesic conversion is the process of calculating equivalent doses between different opioid medications based on their relative potency compared to morphine. This is essential when rotating between opioids (switching from one to another) due to inadequate pain control, intolerable side effects, or changes in route of administration. The concept relies on equianalgesic tables that express each opioid's potency as a ratio to oral morphine, known as the morphine milligram equivalent (MME) factor.
How to Convert Between Opioids
The conversion process follows three steps: (1) Calculate the total daily dose of the current opioid. (2) Convert to daily oral morphine equivalents (MME) by multiplying by the source opioid's MME factor. (3) Divide the MME by the target opioid's MME factor to get the equianalgesic dose. A critical safety step is then reducing the calculated dose by 25–50% to account for incomplete cross-tolerance — the phenomenon where tolerance to one opioid does not fully transfer to another.
Understanding MME Thresholds
The CDC Clinical Practice Guideline (2022) uses morphine milligram equivalents to quantify opioid exposure and guide prescribing. Doses ≥50 MME/day warrant caution and reassessment, while ≥90 MME/day represents high risk for overdose and death. These thresholds were developed primarily for chronic non-cancer pain. Cancer pain, acute pain, and end-of-life care may require different considerations, and clinical judgment should always guide dosing decisions.
🔑 Clinical Pearls
- Methadone has a uniquely long and variable half-life (8–59 hours). Its conversion ratio to morphine is NOT linear — it increases with higher morphine doses, making high-dose conversions particularly dangerous.
- Fentanyl patches deliver medication over 72 hours. Full analgesic effect takes 12–24 hours after application. Converting from patches requires calculating the daily MME first (mcg/hr × 2.4).
- Elderly patients and those with renal or hepatic impairment may need additional dose reductions beyond the standard 25–50% cross-tolerance adjustment.
- Always consider non-opioid adjuncts (acetaminophen, NSAIDs, gabapentinoids, regional anesthesia) to minimize opioid requirements.
Key References
- CDC Clinical Practice Guideline for Prescribing Opioids for Pain. MMWR. 2022;71(No. RR-3):1-95.
- American Pain Society. Principles of Analgesic Use in the Treatment of Acute Pain and Cancer Pain. 7th ed. 2016.
- Fine PG, Portenoy RK. Establishing "best practices" for opioid rotation. J Pain Symptom Manage. 2009;38(3):418-425.
- CMS Opioid Oral Morphine Milligram Equivalent (MME) Conversion Factors. Centers for Medicare & Medicaid Services.
Formula last verified: February 2026