desvenlafaxine will raise the level or influence of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Caution/Keep track of. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, four hundred mg) decrease the CYP2D6 substrate dose by approximately 50%; no dosage adjustment wanted with desvenlafaxine doses seven consecutiv