T3 to T4 equivalence question

I have been on T3 only now for around 10 weeks after previously being on T4 for 17 yrs, and then T3/T4 for a short while.

Despite being given the go ahead by my endo (but then discharged), and prescribed by my GP (who knows nothing), I am pretty much alone in this. I am using online support groups and books to get info.

I am just puzzled re the equivalence issue and how much eventually I should be taking. I was on 100mcg T4, and T3 is supposed to be equivalent I was told to about 3x a T4 dose. However I see on Dr Myhill's site she says it's equivalent to 5 x which I am a bit surprised by...


(see paragraph on Some People Only feel Well using Pure T3). She mentions Tertroxine though so maybe that's a different kind of T3? (slow release?)

Anyway, to get to the point..... I am now up to 40mcg of T3 which is equivalent to at least 120mcg. How do I know when to stop adding it in? My BP and temp are not normal yet as far as I can see ..... at least not all the time. They are up and down at the moment to be honest. Also my symptoms are no better. I have a diagnosis of CFS and I feel now that it's not just about the thyroid and adrenals (I am doing the circadian dose of T3 to help the latter).... though I am prepared to keep trying for a bit longer.

I have asked Paul Robinson on another board and he says the thinks I am still hypothyroid and to keep going, but I am unsure how long to keep going for. In his book and Dr Myhill seem to think that you would feel better long before this!

Any thoughts on this would be gratefully listened to.

4 Replies

  • Any equivalence between T4 and T3 is a rough estimate based on what some other people found. Yes - there is some science behind it as well, but those differences between people keep being all too important. Yes - it helps to give you some idea of what to expect. But you need what you need regardless of any arithmetic.

    The Summary of Product Characteristics for Liothyronine in the UK (Mercury Pharma) says this:

    Adults: Starting dose of 10 or 20 micrograms every 8 hours, increasing after one week, if necessary, to the usual recommended daily dose of 60 micrograms in two or three divided doses.


    So, on that basis, 40 micrograms is indeed quite possibly not enough. Quite possible you are still hypothyroid. And some people need very much greater doses.

    A few years ago liothyronine was sold under the branding Tertroxin, but then that was changed so it is now officially a generic product called Liothyronine. However, the actual tablets did not a change at all. You can see that on the SPC linked above.

    There is no other licensed oral liothyronine product in the UK.


  • Everyone differs in their particular dose which makes them feel well.

    When taking thyroid gland hormone replacements, the question 'Am I on enough' should be 'How do I feel'. If you don't feel you have reached optimum, you should increase your dose gradually. If you feel overstimulated, you just miss the next day's dose and return to the previous one. This is a link which may be helpful - you can also see how high a dose can be for a particular person. Dr Lowe has also two excerpts:-

    First, the belief that timed-released T3 is of any advantage over plain T3 (such as Cytomel) is simply false. My understanding of the processing and action of T3 in the body leaves me without a plausible explanation of how timed-release T3 might be superior. Some physicians have told me that timed-released T3 ". . . avoids the cardiac arrhythmias caused by plain T3." My response is that I've done hundreds of series of ECGs on patients taking plain T3, but I've never seen such arrhythmias. (See "Important Issues") The argument that the use of timed-release T3 avoids arrhythmias is a theoretical notion without objective substantiation (there are no studies that show this!


    And finally, why do I specify that the typical patient use one full dose of non-timed-release Cytomel for life? Because extensive testing has shown that this is safe, effective, and most economical—when used within the context of our entire protocol.


  • Are you sure that you were on the right dose of T4? 100 mcg is quite a small dose, and you still have symptoms, CFS is a bunch of hypo symptoms that haven't been resolved, so maybe 100 wasn't enough for you.

    The important thing is how you feel. If you don't feel good, add more. If you feel fine, stop there. After all, when your thyroid was working it didn't work out how much T3 is equal to how much T4, it just pumped out what you needed to live well.

    T3 to T4 equivalence is just a rough guide. It's not an exact science. And if you have trouble converting T4 to T3, then it's pretty meaningless. Don't worry, you'll know if you start to go over.

    Hugs, Grey

  • Thank you all for your replies. Very much appreciated!

    I think I am just concerned as I am doing it alone, but not sure at which time the GP is going to maybe call me to account over the rising dosage, and it's helpful to have that info from emc Rod, so I will print that out and have it to hand if she queries it.

    I know that some people on thyroid forums consider that CFS is JUST 'a bunch of hypo symptoms', and of course CFS is just a bunch of symptoms it's true, but I am not at all convinced that they are all to do with the thyroid. I think it's a lot more complex than that (having spent the last few years looking at ME/CFS research before I even ended up on thyroid forums.) I think it's entirely likely that there are people diagnosed with CFS who do in fact have unresolved thyroid issues. However if it were that simple I don't think that they would still be spending millions on research for ME/CFS.

    That said, I will continue for now with T3 increasing the dose and see how things progress for me, since yes, it is quite possible that for now I am hypothyroid still.

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