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Clinical data
SynonymsSemorphone, Mr 2264
CAS Number
PubChem CID
E number{{#property:P628}}
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Chemical and physical data
Molar mass345.39 g/mol

Semorphone (Mr 2264) is an opiate analogue that is an N-substituted derivative of oxymorphone.

Semorphone is a partial agonist at μ-opioid receptors. It is around twice the potency of morphine, but with a ceiling effect on both analgesia and respiratory depression[1] which means that these effects stop becoming any stronger after a certain maximum dose.

It is not currently used in medicine, and is not a controlled drug, although it might be considered to be a controlled substance analogue of oxymorphone on the grounds of its related chemical structure in some jurisdictions such as the USA, Canada, Australia and New Zealand.


  1. Behne M, Bremerich D, Heinrich J, Schumacher H, Scherer M. Respiratory effects and tolerability of Mr 2264 Cl. A new opiate partial agonist in comparison with morphine and placebo. European Journal of Clinical Pharmacology. 1994;46(4):301-4.

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