Methadone to Morphine Milligram Equivalent Conversion

Calculation Guidelines

• The National Comprehensive Cancer Network (NCCN) guidelines recommend a methadone-to-morphine conversion ratio of 4:1 for methadone doses in the range of 1-20 mg/day 1
• For methadone doses of 21-40 mg/day, the NCCN guidelines recommend a conversion ratio of approximately 8:1 2
• The total daily methadone dose of 21.25 mg can be converted to a Morphine Milligram Equivalent (MME) dose of approximately 57-86 MME/day using a conversion ratio of 4:1 to 8:1 1

Conversion Ratio Variability

• The methadone-to-morphine conversion ratio increases with higher methadone doses, with a ratio of approximately 4:1 for doses 1-20 mg/day, 8:1 for doses 21-40 mg/day, 10:1 for doses 41-60 mg/day, and exceeding 12:1 for doses >100 mg/day 1, 2, 3

Critical Safety Considerations

• The NCCN guidelines warn that these conversion ratios should never be used in reverse (converting methadone to other opioids) due to methadone's long half-life and risk of accumulation 1, 2
• When converting from methadone to another opioid, a conservative 1:1 ratio should be used initially, with frequent dose adjustments as methadone clears from the system 2