desvenlafaxine will raise the level or result of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Watch. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, 400 mg) lessen the CYP2D6 substrate dose by as much as fifty%; no dosage adjustment required with desvenlafaxine doses 7 consecutive days instantly prior to