I had a bit of a journey myself, like many on the forum. 1st Levo only. A while later some T3 added - a big improvement. Then various NDTs and, hopefully and finally, after a couple of T3s am on T3 only. We have to have trial and error. Sometimes the first thing we decide to alter/change works and others have to try various ones.
I think that fillers/binders in products can affect us and not the hormone it contains. Keeping in mind I'm not medically qualified but I think that doctors don't realise how different makes etc can affect us patients. That's why it is recommended to give a lengthy trial to whatever we decide and sometimes it can be a small increase which can make the difference between feeling awful or good.
T3 proper name is liothyronine. Your doctors will know this name, I hope! Without it we'd die as it is the driving force for our metabolism and enables heart, brain and everything else to function. T4 (levothyroxine) is inactive and has to be convert to T3 and we don't always do so efficiently if T4 dose is too low or we have a defective gene which doesn't allow this to happen.
The link Shaws gave you is a very useful one. Bear in mind that your symptoms and test results may also be a consequence of insensitivity to thyroid hormone. You may be able to follow other links from the one Shaws gave, which will explain more about this.
TSH doesn't necessarily rise in these circumstances. I'm about to go out for the rest of the day, but I'll try to answer at greater length as soon as I can.
T3 alone is used to treat THR - no T4 at all. You would have to carefully wean yourself off levo first, gradually adding in more T3. I've not done it this way myself, so I can't really advise on how to alter your doses of each hormone while you do this.
I'm not saying that you do have THR, just that it's a good idea to consider the possibility.
It's a complicated subject. One good source of info is this:
The link mainly concerns the inherited forms of resistance to T3. However, there are many possible causes and one can acquire insensitivity to thyroid hormone. That was John Lowe's main area of interest, though he himself may have had an inherited form of THR.
I've just returned home from an afternoon out, so I haven't yet had the chance to go through Dr Lowe's main book (The Metabolic Treatment of Fibromyalgia). In his shorter book, Your Guide to Metabolic Health, he refers to the problem of "partial peripheral cellular resistance to thyroid hormone" and describes it as being (in his experience) common among hypothyroid patients with fibromyalgia, and "far from rare among other hypometabolic patients." (p. 147)
I could send you a PM with more information in a couple of days, when I've had a chance to read through the relevant sections of his books.
In that case, THR may not be your problem. You may need to look at adrenal function and/or address nutritional deficiencies, especially B12, D, ferritin.
I am rectifying deficiencies. In fact all of those are OK now, they were not very bad in the first place. My ferritin is low, but otherwise my iron panel is OK. I have an MTHFR mutation and I am at risk of building up serum iron when supplementing instead of building up ferritin.
I will test the adrenals.
However, browsing through my pregnancy labs I found out that I was asymptomatic with a lower FT4 level, no matter what my FT3 level was.
For instance, I was very hypo at FT4 15.80 (12-24) and FT3 4.10 (3.10-7.80) but only a month later after a 7-day synthetic T4 stop and then restart I was feeling good at FT4 13.10 (12-24) and FT3 3.40 (3.10-7.80).
I was on T4 only during pregnancy only 7 months ago.
I know these levels and corresponding symptoms for sure as I was keeping a log during pregnancy, I am keeping one now as well for reference. It is an useful thing.
I know levels in pregnancy differ and in third trimester get lower. I know this for sure since I had a healthy thyroid function during my first pregnancy and my levels were this low in the third trimester as well and I was euthyroid.
Point is I might have some sort of competition going on between T4 (and even rT3 produced by it) and T3 for the cells.
However going T3 only did not alleviate my hypo symptoms, instead it made me ill, I don't even want to remember it.
Yes, for sure I wasn't taking enough T3, I just was not able to tolerate it.
And by the way I have noticed that when I have T4 in my system I can tolerate bigger doses of T3. When I don't have T4 in my system even a small dose of T3 makes me jittery and elevates my heart rate, because it throws me through over-stimulation and severely hypo since I have no "cover" from T4 and T3 acts very abruptly on my system.
I really don't know how to overcome that, I was multi-dosing and still was feeling going though huge peaks and slumps. It was awful.
And looking at my pregnancy labs, I can see I felt best with a TSH of about 1.6-1.9, and a low FT4. I was not under-medicated at all.
In fact TSH is a tool for T4/T3 conversion. The more it falls down, the more conversion slows down... My pregnancy labs are a proof.
One more question: does rT3 have to be at the bottom of the range or below range in order for a person not to have rT3 dominance?
Mine was 143 (90-215) and I was felling pretty ill.
I though rT3 was not a problem. But now I don't know.
You've found that TSH is a tool for you, but many of us have not found it so useful, unfortunately.
In terms of problems treating with T3 alone, or with NDT, you might find the latest STTM newsletter interesting, even if you conclude that it doesn't apply to you:
Dr Lowe does not look at rT3 or rT3/FT3 ratio as a possible problem, hindrance to thyroid therapy? Was that the case?
As far as TSH is concerned, I think I have to concentrate more on FT4/FT3 ratio. It is noticeable that during pregnancy I felt euthyroid with a lower FT4 level, given the TSH level was one and the same.
I have tried lowering my FT4 level two months ago by using T3 only but did not get any better. That is why I assumed TSH has something to do with my well-being, although I might be totally wrong. It has to do with FT4/FT3 levels though.
I don't think FT4 levels should get above mid-range.
Dr Lowe didn't dismiss the role of rT3, because it is a specific product of T4 deiodination. He actually writes quite a lot about deiodination in his main book. However, he did take issue with Dr Wilson and others who place great emphasis on its role in hypothryoidism.
I'll have to get back to you later with more information from Dr Lowe's books, because I'm having quite a busy day and not feeling too well.
Yes, that is what I meant: that Dr Lowe does not put such a great emphasis on rT3 role in hypothyroidism. He even states that calculating a rT3/FT3 ratio is almost impossible since the two levels fluctuate greatly throughout the day and night.
Dr Wilson's view is very categorical.
That in mind, I am still going back and forth between wondering whether I have a rT3 problem or not... I don't know what to think anymore since I am not getting even mildly better on T4, T4/T3 or T3 only.
I was very ill during my pregnancy as well, and got better (even completely fine) by lowering my FT4 level. Even my FT3 level did not matter that much at that time. Lowering my FT4 level and keeping it under 15 (12-24) was the pivotal point in my recovery back then.
I am still wondering whether my unsuppressed TSH had any role to play in that...
And my recovery was remarkably fast. In a matter of 3-4 days at most, when FT4 fell down, I felt fine. (Yes, FT4 level was falling down that fast)
But that was during pregnancy, and I just cannot succeed in doing this now.
I had a similar problem, my results suggested I should be doing OK but I still felt poorly. To cut a long story short, I had a magnesium deficiency. Its very common in people with fibromyalgia and the symptoms mimic hypothyroidism. Unfortunately the NHS only test serum levels of magnesium which is unhelpful as a feedback system maintains serum levels at the expense of cellular levels. I had a private test done by medicheck to see what red cell levels were doing and sure enough my levels were low. Now on magnesium supplementation and I'm beginning to feel better.
I also tested low for vitamin D and ferritin, but clearly it was the magnesium deficiency causing my main problems. Its always worth getting tested for various deficiencies to rule them out. I would strongly recommend getting the red cell magnesium checked, its a very overlooked but vital mineral.
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Am I able to convert ft4 to ft3?
Diarrhoea, high ft3 low ft4.
Low FT4 High FT3
Ft4 over range 
