Calculation of Oral Morphine Equivalents (OME)

Overview

Oral Morphine Equivalents (OME) are approximations of the equianalgesic effects of other opioids compared to oral morphine. Thus, OMEs indicate how much of the reference drug oral morphine would be required to treat pain as effectively as the opioid morphine is compared with. This approach allows for the comparison of different opioid treatments for pain.

Opioid equivalence solely refers to analgesic potency, the ability to treat pain and does not allow for the direct comparison of risks of opioid-related adverse events such as sedation or respiratory depression. This becomes most obvious when looking at the equivalence factors for neuraxial (spinal and epidural) administration of opioids:  neuraxial administration of opioids reduces pain very effectively while being comparatively less likely to cause respiratory depression or sedation.

Other related abbreviations are morphine milligram equivalents (MMEs) and, when describing OME or MME per day, morphine equivalent daily dose (MEDD).

Purpose of Oral Morphine Equivalence (OME) calculations

• OME calculations help identify opioid tolerance in individual patients. The FDA defines an opioid-tolerant patient as receiving for 1 week or longer at least 60 mg oral morphine/day or an equianalgesic dose of another opioid.
• OME calculations facilitate monitoring changes in opioid utilization over time. For this reason, UCSF employs an OME calculator in the APEX Pain Summary. 
• OME calculations are needed to identify the need for mandated naloxone prescriptions when opioids are prescribed.
• OME calculation allows for the comparison of different opioids for research or for monitoring purposes.

Opioid Equivalence Factors used at UCSF​