desvenlafaxine will increase the level or influence of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Check. Desvenlafaxine inhibits CYP2D6; with better desvenlafaxine doses (ie, four hundred mg) minimize the CYP2D6 substrate dose by up to fifty%; no dosage adjustment needed with desvenlafaxine doses 7 consecutive times immediat