The study is good and so valid. However, I suspect many people who need T3 have a pituitary that is underperforming and so their TSH falls more quickly. There is evidence that TSH stimulates deiodinase, so a subnormal TSH would lead to a need for T3.
I just know that when I was first put on T3 with just a small 5 mcg twice a day my TSH went to .01 and not changed even with a higher dose of T3. My thyroid is atrophied and no longer working at all.
Do you have your blood test results from before and after you started T3 and what doses of T3, T4 were you taking? What was your TSH just before you started T3?
TSH was 2.293 and FT4 was over range @ 1.7 FT3 low in range @2.6. My TSH started fluctuating dramatically for the two previous years prior to this where in the past it was pretty stable. First introduced to T3 my TSH .011, FT4 1.67 and FT3 3.9. This was a sweet spot to be sure because my Endo had not lowered my dose of T4 when she added the T3 and all hell broke loose that fall. My FT4 went over range to 1.95 and my FT3 lowered to 3.4 but my RT3 was 60.2 and let me tell you I felt like death warmed over! I had to stop all T4 and slowly add T3 in to feel some sort of normal. It took 2 years of T3 only because when I would try to introduce T4 back in my RT3 would climb and go over range. Fast forward those 2 years and eventually I lowered my T3 and added the T4 back in. My dose now is 25mcg T3 and 75 mcg T4 (Tirosint). I've been on this dose since for 4 years now. My TSH has pretty much stayed at .01 since late 2015 when first introduced to T3.
It seems your thyroid went a bit bonkers around the time you started T3 as you wouldn't expect fT4 to go up. Your current dose is equivalent to about 150 mcg levothyroxine which isn't a big amount.
Not everyone has suppressed TSH on T3. I take combined treatment levothyroxine T4 and liothyronine T3. My TSH is always just about in range along with my T4 and T3 levels being in range. I feel symptom free.
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