desvenlafaxine will boost the level or result of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Watch. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, 400 mg) minimize the CYP2D6 substrate dose by as many as fifty%; no dosage adjustment wanted with desvenlafaxine doses seven consecutive days straight away b