desvenlafaxine will boost the stage or influence of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Check. Desvenlafaxine inhibits CYP2D6; with larger desvenlafaxine doses (ie, 400 mg) lower the CYP2D6 substrate dose by around fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days quickly previous to tak