desvenlafaxine will enhance the amount or impact of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Keep track of. Desvenlafaxine inhibits CYP2D6; with greater desvenlafaxine doses (ie, 400 mg) decrease the CYP2D6 substrate dose by up to fifty%; no dosage adjustment wanted with desvenlafaxine doses seven consecutive days instantl