desvenlafaxine will improve the level or influence of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Keep track of. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, 400 mg) reduce the CYP2D6 substrate dose by nearly fifty%; no dosage adjustment required with desvenlafaxine doses seven consecutive times promp