desvenlafaxine will raise the amount or impact of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Caution/Observe. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, 400 mg) lessen the CYP2D6 substrate dose by as many as fifty%; no dosage adjustment wanted with desvenlafaxine doses 7 consecutive times instantly before