desvenlafaxine will boost the stage or effect of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Monitor. Desvenlafaxine inhibits CYP2D6; with increased desvenlafaxine doses (ie, four hundred mg) decrease the CYP2D6 substrate dose by approximately fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days pr