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