desvenlafaxine will raise the level or result of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Caution/Watch. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, four hundred mg) decrease the CYP2D6 substrate dose by nearly 50%; no dosage adjustment wanted with desvenlafaxine doses seven consecutive times instantly pr