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Systematic (IUPAC) name
(5α)-4,5-Epoxy- 3,14-dihydroxy- 17-(2-methoxyethyl) morphinan- 6-one
CAS Number 88939-40-6
ATC code none
PubChem CID 5491906
Chemical data
Formula C19H23NO5
Molar mass 345.39 g/mol[[Script error: No such module "String".]]
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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.


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  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.