desvenlafaxine will enhance the stage or impact of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Check. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, 400 mg) lower the CYP2D6 substrate dose by as much as fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days straight away just b