desvenlafaxine will boost the degree or result of codeine by influencing hepatic enzyme CYP2D6 metabolism. Use Warning/Monitor. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, 400 mg) lower the CYP2D6 substrate dose by approximately fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive days quickly previo