desvenlafaxine will boost the stage or effect of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Desvenlafaxine inhibits CYP2D6; with bigger desvenlafaxine doses (ie, 400 mg) lessen the CYP2D6 substrate dose by approximately 50%; no dosage adjustment desired with desvenlafaxine doses 7 consecutive days straight away ahea