Morphine Equivalent Conversion Factors for Common Opioids
The CDC 2022 guidelines provide standardized conversion factors to calculate morphine milligram equivalents (MME): oxycodone uses a 1.5 conversion factor, hydrocodone uses 1.0, and transdermal fentanyl uses 2.4 (mcg/hr). 1
Standard Conversion Factors
The following conversion factors should be multiplied by the daily opioid dose to determine MME 1:
- Hydrocodone: 1.0 - meaning hydrocodone mg equals morphine mg on a 1:1 basis 1
- Oxycodone: 1.5 - meaning 20 mg oxycodone daily equals 30 MME daily 1, 2
- Fentanyl transdermal: 2.4 - applied to mcg/hr (NOT mg/day), so a 25 mcg/hr patch equals 60 MME daily 1
- Hydromorphone: 5.0 - making it 5 times more potent than morphine 1
- Methadone: 4.7 - though this requires particular caution due to variable half-life 1
- Codeine: 0.15 - making it much weaker than morphine 1
- Tramadol: 0.2 1
- Tapentadol: 0.4 1
- Oxymorphone: 3.0 1
Practical Calculation Examples
For hydrocodone: A patient taking hydrocodone 5 mg four times daily (20 mg total) equals 20 MME daily 1
For oxycodone: Extended-release oxycodone 10 mg twice daily (20 mg total) equals 30 MME daily (20 mg × 1.5 = 30 MME) 1
For transdermal fentanyl: A 75 mcg/hr patch equals 180 MME daily (75 × 2.4 = 180 MME) 1
Critical Safety Warnings When Using These Conversions
These conversion factors are estimates ONLY and cannot account for individual variability in genetics and pharmacokinetics. 1
When Converting Between Opioids (Opioid Rotation):
- Never use the calculated MME dose directly when switching opioids - the new opioid should typically be dosed 25-50% lower than the calculated equianalgesic dose to avoid overdose from incomplete cross-tolerance 1, 2
- Always provide breakthrough medication during the conversion period, typically 10-20% of the total daily dose as short-acting opioid 3, 4
Special Cautions for Specific Opioids:
Methadone requires extreme caution because 1:
- It has a long and variable half-life
- Peak respiratory depression occurs later and lasts longer than peak analgesia
- The 4.7 conversion factor is a rough estimate and may underestimate methadone's potency at higher doses
Transdermal fentanyl requires particular attention because 1:
- It is dosed in mcg/hr, not mg/day (a common source of fatal errors)
- Absorption is affected by heat, fever, and other factors
- It takes 12-24 hours to reach therapeutic levels 3
- The previous opioid should be maintained during the first 12-24 hours of patch application 3
Buprenorphine is not included in standard conversion tables because it is a partial μ-receptor agonist with ceiling effects, making it fundamentally different from full agonists 1
Clinical Dosing Thresholds
The CDC defines opioid dose categories as 1, 5:
- Low dose: Up to 40 MME/day
- Moderate dose: 41-90 MME/day
- High dose: ≥91 MME/day
Before increasing total opioid dosage to ≥50 MME/day, clinicians should pause and carefully reassess individual benefits and risks, as many patients do not experience benefit in pain or function from doses above this threshold but face progressively increasing risks 1
Route of Administration Conversions
IV/IM morphine to oral morphine: The conversion ratio is approximately 1:3, meaning 10 mg IV morphine equals 30 mg oral morphine 4, 6
IV fentanyl to IV morphine: Use a 100:1 ratio, meaning 100 mcg IV fentanyl equals 10 mg IV morphine 4
Continuous IV fentanyl infusion to transdermal fentanyl: Use a 1:1 ratio where mcg/hr of IV fentanyl equals mcg/hr of transdermal fentanyl 3
Common Pitfalls to Avoid
- Confusing mcg/hr with mg/day for fentanyl patches - this is a potentially fatal error 1
- Using conversion tables to switch FROM fentanyl or methadone to other opioids - these conversions are intentionally conservative in one direction only 6
- Failing to reduce the calculated dose by 25-50% when rotating opioids - incomplete cross-tolerance means the full equianalgesic dose may cause overdose 1, 2, 4
- Not accounting for renal insufficiency with morphine - active metabolites accumulate and can cause neurotoxicity 2