- Serum concentrations of venlafaxine and its metabolites O-desmethylvenlafaxine and N-desmethylvenlafaxine in heterozygous carriers of the CYP2D6*3, *4 or *5 allele. Hermann, M., Hendset, M., Fosaas, K., Hjerpset, M., Refsum, H. Eur. J. Clin. Pharmacol. (2008)