desvenlafaxine will boost the degree or influence of codeine by impacting hepatic enzyme CYP2D6 metabolism. Use Warning/Observe. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, 400 mg) minimize the CYP2D6 substrate dose by up to 50%; no dosage adjustment desired with desvenlafaxine doses seven consecutive times straight away a