What happens to synthetic T4 when you take T3?

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I was wondering what would happen to synthetic T4 if you start to take T3? Does the body detect the T3 and stop converting the (or lower the conversion rate of the) T4 to T3 & use it for other purposes (e.g. RT3)? Or would it continue to convert the T4 as per normal?





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  • Posted

    What a brilliant question!

    There is a very good paper by Gregg Kelly who explains all of the organic chemistry associated with these processes. I'm sorry I can't give you the link because for some reason links arn't allowed.

    Refering to Kelly's figure 3 one would conclude that any excess of T4 would be made into rT3 - but that is not all bad since rT3 can be converted into T2 (which I think has something to to with the immune system - well according to Wiki). T4 would be in excess since it is not required to be converted into T3 - since you are taking that externally.

    Now, does your T3 production shut down? This will depend upon two factors, one, can you convert in the first place and secondly IS the presence of T3 detected by the pituatory or hypothalamus. We all agree that T4 is detected but what about T3? Who knows?

    If it is detected then yes I believe it will shut down production of T3 upon detecting an overload.

    If it is not detected then I see no reason that the thyroid or any other periferal organ (particularly the liver) would stop conversion.

    Your symptoms however would stop the process. If you are bubbling over with super high T3, you are going to be so hyper that you will just not stick another pill in your mouth! And don't worry, T3 only lasts about 6 hours +/- so if you can last 6 hours, you will be OK.

    HOWEVER do not do this experiment at home!

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    • Posted

      Thanks for the response! smile

      I would imagine if your TSH (i.e it was surpressed) reflected the fact that T3 was being taken then this means your pituatory has detected this?

      I think I read somewhere that T3 is what changes TSH not T4? I could be wrong though..


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    • Posted

      You know, I wondered about that, in fact I posted a question on this forum in case anyone knew exactly what is detected, T3, T4 or a ratio. Sadly I just got the obvious answer, T4. I am so glad someone else is thinking about this. An accurate answer could change a lot of things - but then the  existing, simple working solutions don't seem to get our medical profession very far so I won't hold my breath.
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    • Posted

      Gosh, I am so sorry, so you did!

      Hoggle, did you notice that? It'a a really good paper. You may have to read it more than once (I read it three times) and you might have to stop and look up some terms but it is well worth the effort and may answer your quesiton.

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