There is a fairly rare (and debatable) condition, known as thyroid hormone resistance, where supposedly the cells do not adequately take up the hormone. Sometimes these individuals are treated w/"supraphysiological doses" of T4, that is, more than what the body would produce under normal circumstances.
This concept may be similar to that of "insulin resistance," except that IR is generally accepted by the allopathic med community, while THR is not.
John Lowe has written extensively on his theory that fibromyalgia is due to metabolic & endocrine disorders, of which THR is one. He has another book due out next month entitled "Speeding up to Normal." I believe he also sometimes uses supraphys. dosing for fibromyalgia.
There have been published studies, mostly European, of the successful use of supraphysiologic dosing of T4 for individuals suffering from depression and bipolar disorder that is refractory to treatment with standard meds. Some of these individuals had fairly normal blood tests; most tolerated the treatment well & did not show the usual signs of hyperthyroidism. Perhaps they suffered a type of THR as well.
It is important to note that what I have described above are cases which are atypical from the "usual" hypothyroid presentation. Medical supervision is a must for increased dosages of TH. Physical harm can arise from a dosage that is too high for one's unique physiology.
An example of this is a local psychiatrist who found that he had better patient response to psych meds with extra T3 & T4 added to the regimen. Many people needed less of the psych meds, and hence suffered fewer side effects. Many people had a return of functionality that had been lost for decades. The doc used low/normal type doses, but note that not all individuals were hypoT by standard testing. He helped many people, but along the way encountered an one person who had a severe adverse reaction, enough to convince the doc that "it was not worth it, " even though many were helped.
I realize most of you here on this board won't relate to this info, but it's interesting ...