What is MME (Morphine Milligram Equivalent)?
MME is a standardized metric that converts different opioid doses into an equivalent amount of morphine, allowing clinicians to compare the relative potency of various opioids and calculate total daily opioid exposure. This conversion system is essential for assessing overdose risk, as mortality increases progressively with higher MME doses 1.
How MME Works
To calculate MME, multiply the daily dose of any opioid by its specific conversion factor 1. For example:
- Hydrocodone 5 mg taken 4 times daily = 20 mg total daily dose × 1.0 conversion factor = 20 MME/day
- Oxycodone 10 mg extended-release taken twice daily = 20 mg total daily dose × 1.5 conversion factor = 30 MME/day
Standard Conversion Factors (2022 CDC Guidelines)
The most current conversion factors are 1:
| Opioid | Conversion Factor |
|---|---|
| Morphine | 1.0 |
| Codeine | 0.15 |
| Hydrocodone | 1.0 |
| Oxycodone | 1.5 |
| Hydromorphone | 5.0 |
| Oxymorphone | 3.0 |
| Fentanyl transdermal (mcg/hr) | 2.4 |
| Methadone | 4.7 |
| Tramadol | 0.2 |
| Tapentadol | 0.4 |
Critical Clinical Caveats
MME calculations are estimates only and cannot account for individual genetic variability or pharmacokinetics 1. Several important warnings:
Never use MME calculations to directly convert between opioids for prescribing purposes—the new opioid must be dosed substantially lower than the calculated MME to avoid overdose due to incomplete cross-tolerance 1
Methadone requires extreme caution due to its long, variable half-life where respiratory depression peaks later and lasts longer than analgesia 1
Fentanyl transdermal is dosed in mcg/hr (not mg/day) and absorption varies with heat and other factors 1
All doses are mg/day except fentanyl which is mcg/hr 1
Clinical Application for Risk Assessment
The CDC uses MME thresholds to stratify overdose risk 1:
≥50 MME/day: Pause and carefully reassess individual benefits versus risks before any increase—many patients show no additional benefit in pain or function at this threshold but face progressively increasing overdose risk 1
>50 MME/day: Dosage increases beyond this point yield diminishing returns for pain relief while exponentially increasing mortality risk 1
Starting dose for opioid-naïve patients: 20-30 MME/day (equivalent to hydrocodone 5 mg four times daily) 1
Important Limitations
MME conversions have significant definitional variability in research and clinical practice—the same prescription can yield 3-fold differences in calculated daily MME depending on which calculation method is used 2. This creates substantial heterogeneity when comparing studies or surveillance data. Additionally, tramadol and tapentadol have mixed mechanisms (μ-receptor agonism plus reuptake inhibition), so their overdose risk may not follow the same dose-dependent pattern as pure μ-agonists 1.
The MME system provides a practical framework for monitoring cumulative opioid exposure and overdose risk, but must be applied with clinical judgment recognizing its inherent limitations as an estimate rather than a precise measurement 1.