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CAS Number
PubChem CID
E number{{#property:P628}}
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Chemical and physical data
Molar mass249.349 g/mol
3D model (JSmol)

O-Desmethyltramadol (M1) is an opioid analgesic which is made in the body from tramadol.[1]

(+)-O-Desmethyltramadol is the most important metabolite of tramadol produced in the liver after tramadol is consumed. This metabolite is considerably more potent as a μ opioid agonist than the parent compound,[2] and indeed is so much more potent[3] that tramadol can to some extent be regarded as a prodrug for O-desmethyltramadol in the same way that codeine is a prodrug for morphine.

Tramadol is demethylated by the liver enzyme CYP2D6[4] in the same way as codeine, and so similarly to the variation in effects seen with codeine, individuals who have a less active form of CYP2D6 ("poor metabolisers") will tend to get reduced analgesic effects from tramadol.

The two enantiomers of O-desmethyltramadol show quite distinct pharmacological profiles;[5] both (+) and (-)-O-desmethyltramadol are inactive as serotonin reuptake inhibitors,[6] but (-)-O-desmethyltramadol retains activity as a dopamine and noradrenaline reuptake inhibitor[7] and so the mix of metabolites produced contributes significantly to the complex pharmacological profile of tramadol.


  1. Sevcik J, Nieber K, Driessen B, Illes P. Effects of the central analgesic tramadol and its main metabolite, O-desmethyltramadol, on rat locus coeruleus neurones. British Journal of Pharmacology. 1993 Sep;110(1):169-76.
  2. Dayer P, Desmeules J, Collart L. Pharmacology of tramadol. Drugs. 1997;53 Suppl 2:18-24. (French)
  3. Lai J, Ma SW, Porreca F, Raffa RB. Tramadol, M1 metabolite and enantiomer affinities for cloned human opioid receptors expressed in transfected HN9.10 neuroblastoma cells. European Journal of Pharmacology. 1996 Dec 5;316(2-3):369-72.
  4. Borlak J, Hermann R, Erb K, Thum T. A rapid and simple CYP2D6 genotyping assay--case study with the analgetic tramadol. Metabolism. 2003 Nov;52(11):1439-43.
  5. Garrido MJ, Valle M, Campanero MA, Calvo R, Troconiz IF. Modeling of the in vivo antinociceptive interaction between an opioid agonist, (+)-O-desmethyltramadol, and a monoamine reuptake inhibitor, (-)-O-desmethyltramadol, in rats. Journal of Pharmacology and Experimental Therapeutics. 2000 Oct;295(1):352-9.
  6. Bamigbade TA, Davidson C, Langford RM, Stamford JA. Actions of tramadol, its enantiomers and principal metabolite, O-desmethyltramadol, on serotonin (5-HT) efflux and uptake in the rat dorsal raphe nucleus. British Journal of Anaesthesia. 1997 Sep;79(3):352-6.
  7. Driessen B, Reimann W, Giertz H. Effects of the central analgesic tramadol on the uptake and release of noradrenaline and dopamine in vitro. British Journal of Pharmacology. 1993 Mar;108(3):806-11.

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