the meds are organic forms of Iodine - molecules that have carbon in them. most organic forms of Iodine are highly toxic. thats why they go to pigs to make none toxic thyroid hormones like the thyroid does and why most people do best on the armour.
the reason they work and not plain Iodine alone is that the work the thyroid would do to make the molecules is already done. if the thyroid can be jump started into making them again, all or in part, then the meds can be decreased or stopped.