What is MME?
Morphine Milligram Equivalent (MME), also known as Morphine Equivalent Dose (MED), is a standardized way to express the potency of different opioid medications in terms of an equivalent dose of oral morphine. Since opioids vary widely in their potency, MME provides a common metric that allows clinicians, pharmacists, and researchers to compare dosages across different opioid formulations.
The concept is essential for patient safety. The CDC and other regulatory bodies use MME thresholds to identify patients who may be at increased risk for opioid-related adverse events, including respiratory depression and overdose death. Higher MME/day values are associated with greater risk.
MME is not a direct measure of pain relief or clinical efficacy; rather, it is a risk assessment tool. Two patients on the same MME/day may have vastly different clinical responses due to individual pharmacokinetic and pharmacogenomic differences.
MME Formula & Conversion Factors
Each opioid has a specific conversion factor that relates it to morphine. The following table lists the standard conversion factors used in clinical practice:
| Opioid | Conversion Factor | Example: 30 mg/day → MME |
|---|---|---|
| Morphine | 1 | 30 MME/day |
| Codeine | 0.15 | 4.5 MME/day |
| Fentanyl transdermal (mcg/hr) | 2.4 | 72 MME/day |
| Hydrocodone | 1 | 30 MME/day |
| Hydromorphone | 4 | 120 MME/day |
| Methadone (1–20 mg/day) | 4 | 120 MME/day |
| Methadone (21–40 mg/day) | 8 | 240 MME/day |
| Methadone (41–60 mg/day) | 10 | 300 MME/day |
| Methadone (≥61 mg/day) | 12 | 360 MME/day |
| Oxycodone | 1.5 | 45 MME/day |
| Oxymorphone | 3 | 90 MME/day |
| Tapentadol | 0.4 | 12 MME/day |
| Tramadol | 0.1 | 3 MME/day |
Methadone Special Considerations
Methadone is unique among opioids because its conversion factor is not fixed — it varies with the total daily dose. This is due to methadone's long and variable half-life (8–59 hours), its accumulation in tissues, and its complex pharmacokinetics including NMDA receptor antagonism.
Methadone 21–40 mg/day → factor 8
Methadone 41–60 mg/day → factor 10
Methadone ≥61 mg/day → factor 12
Because of these complexities, methadone conversions carry higher risk. Clinicians should exercise extra caution when initiating methadone therapy or converting from other opioids to methadone, and vice versa. Incomplete cross-tolerance is a significant safety concern.
Risk Level Interpretation
| MME/day | Risk Level | Clinical Recommendation |
|---|---|---|
| < 50 | Lower Risk | Standard monitoring; lower risk of overdose |
| 50 – 89 | Moderate Risk | Exercise caution; reassess pain treatment plan; consider risk mitigation (e.g., naloxone co-prescribing) |
| ≥ 90 | High Risk | CDC recommends avoiding or carefully justifying; significant overdose risk; co-prescribe naloxone; consider specialist referral |
Research shows that patients receiving ≥90 MME/day have a risk of overdose approximately 2–9 times higher compared to patients on <20 MME/day, depending on the study population.
MME Risk Scale Diagram
CDC Guidelines on Opioid Prescribing
The CDC Clinical Practice Guideline for Prescribing Opioids (updated 2022) provides evidence-based recommendations for prescribing opioids for chronic pain outside of active cancer treatment, palliative care, and end-of-life care:
- Start low: When opioids are initiated, prescribe the lowest effective dose. Avoid starting at ≥50 MME/day.
- Reassess regularly: When increasing dosage to ≥50 MME/day, carefully reassess individual benefits and risks.
- Avoid ≥90 MME/day: Avoid increasing dosage to ≥90 MME/day, or carefully justify the decision to do so with documented clinical reasoning.
- Co-prescribe naloxone: Consider offering naloxone when factors that increase risk for opioid overdose are present, such as dosages ≥50 MME/day.
- Multimodal therapy: Use opioids alongside non-opioid therapies (physical therapy, behavioral therapy, non-opioid medications) when possible.
- Monitor with PDMP: Check Prescription Drug Monitoring Program (PDMP) data before prescribing and periodically during therapy.
Overdose Risk & Prevention
Opioid overdose is a leading cause of injury-related death in many countries. Key risk factors include:
- High daily MME (≥50 MME/day, and especially ≥90 MME/day)
- Concurrent use of benzodiazepines or other CNS depressants
- History of substance use disorder
- Disrupted sleep or sleep apnea
- Renal or hepatic impairment affecting drug metabolism
- Recent dosage increases or periods of abstinence followed by resumption
Naloxone (Narcan) is a life-saving opioid antagonist that can rapidly reverse opioid overdose. It should be co-prescribed for patients at elevated risk, and family members/caregivers should be educated on its use.
Worked Example
A patient is prescribed Oxycodone 20 mg twice daily:
Oxycodone conversion factor = 1.5
MME = 40 × 1.5 = 60 MME/day
This falls in the Moderate Risk range (50–89 MME/day). The clinician should reassess the pain management plan, consider non-opioid alternatives, and discuss naloxone co-prescribing with the patient.
Another example — Methadone:
A patient takes Methadone 35 mg/day:
Methadone 21–40 mg/day → factor = 8
MME = 35 × 8 = 280 MME/day
This is well above 90 MME/day — High Risk. If this is for pain management (not opioid use disorder treatment), careful clinical justification and risk mitigation are essential.
Frequently Asked Questions
Does MME apply to patients on methadone for opioid use disorder (OUD)?
The CDC guideline thresholds are intended for pain management, not for methadone maintenance treatment (MMT) of opioid use disorder. Methadone doses for OUD are titrated based on clinical response and should not be limited by MME thresholds alone.
How do I calculate MME for patients on multiple opioids?
Calculate the MME for each opioid separately, then sum all MME values to obtain the total daily MME. This total is what should be compared against risk thresholds.
Are the conversion factors exact?
No. Equianalgesic ratios are approximate and based on population-level data. Individual responses vary due to genetic factors, tolerance, organ function, and drug interactions. The conversion factors are best used as clinical guides, not precise calculations.
What about fentanyl patches?
Fentanyl transdermal patches are dosed in mcg/hr. The conversion factor of 2.4 directly converts the mcg/hr rate to MME/day. For example, a 25 mcg/hr fentanyl patch = 25 × 2.4 = 60 MME/day.
Should I abruptly reduce high-MME prescriptions?
No. The CDC advises against abrupt opioid discontinuation or rapid dose reduction, as this can cause withdrawal, uncontrolled pain, psychological distress, and may lead patients to seek illicit opioids. Tapering should be gradual and individualized.