desvenlafaxine will boost the level or impact of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Keep an eye on. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, four hundred mg) minimize the CYP2D6 substrate dose by as much as fifty%; no dosage adjustment required with desvenlafaxine doses 7 consecutive days