Check out this diagram for a sense of how complicated the thyroid controls are, and how many different factors are affecting thyroid stimulating hormone (TSH), our basic measure of thyroid function. At least one thing seems clear: TSH is involved in a lot more than just telling the thyroid gland to make more thyroid hormones. Maybe this is why we see dramatic results sometimes with thyroid hormones — somehow the whole TSH system seems to be changed when the hormones come from the outside instead of the inside. Whatever explanation we come up with, it will have to explain why some patients seem to get better even when they start with TSH values that are clearly normal” by standard lab tests.