desvenlafaxine will enhance the level or impact of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, four hundred mg) minimize the CYP2D6 substrate dose by up to fifty%; no dosage adjustment essential with desvenlafaxine doses 7 consecutive days quickly