I self-diagnosed my condition, hypothyroidism, because I had three quarters of the list of symptoms in the Merck Manual. I was tested and was prescribed T4 over my demands for T3, which worked for my mother. It did not work as my doctor waited for the T4 magic to appear.
Then the doctor referred me to my first endocrinologist. He tried to appear to be doing something by prescribed an insignificant dose of T3 and continued the T4 dosage. The T3 provided me some short term relief, but the suffering returned. So, nearing the two-year mark, I saw a second endocrinologist, who reacted to the once a day prescription for T3 and made it three times a day. In two weeks, my active, attractive life returned.
After some years, my body demanded more T3 and I went to a third endocrinologist, who insisted upon a trial of a greater dose of T4 and less T3. It did not work. So I was prescribed, the now proscribed, desiccated thyroid, which worked.
Consequently, I also fit the medically accepted CDR causality test protocol (challenge, de-challenge, re-challenge). T3 does work, at least for some. It works for me. But, in spite of a decade on T3 and over suppressed TSH, I feel that I have always been under dosed, but doctors are afraid of T3. I tell them that I would rather die happy.