desvenlafaxine will raise the stage or outcome of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Warning/Observe. Desvenlafaxine inhibits CYP2D6; with greater desvenlafaxine doses (ie, four hundred mg) minimize the CYP2D6 substrate dose by as many as 50%; no dosage adjustment required with desvenlafaxine doses 7 consecutive days right