desvenlafaxine will enhance the stage or outcome of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Keep an eye on. Desvenlafaxine inhibits CYP2D6; with increased desvenlafaxine doses (ie, four hundred mg) decrease the CYP2D6 substrate dose by as much as 50%; no dosage adjustment necessary with desvenlafaxine doses seven consecut