Is it normal for T4 levels to go down when taking T3 only?

I have been on T3 only for a few months and have seen a massive improvement in my health. Just had my blood tests done for my appointment with the consultant. I'm very keen to stay on the T3 so am hopeful there is nothing about my blood test results that will concern him. They are as follows: T3 - 3.5 pmol/L (3.1-6.8), Serum free T4 below range: 7.6pmol/L (11.0-20.0) and Serum TSH 3.62 (0.3 -5.0).

I'd like to go in to the appointment a bit informed so would welcome any advice on these results and any explanations as to why the T4 has gone down.

Thanks so much.

7 Replies

  • nothing wrong with your bloods, they are 'typical' of someone on T3, however your TSH is quite high for the typical person on T3...either you are on a tiny dose of 20mcg or similar or you did not take your T3 for at least 2 days before your blood test? :D

    My T4 is non existant on T3 that's because I have a suppressed TSH, but yes, T4 will always be low for someone on T3 only and on low-er side for someone on NDT.

  • T4 is the storage hormone, which sits in your blood waiting to be turned into t3. If you aren't taking any then it will run down, taking t3 cannot make the t4 increase.

    Of course if you don't convert then there is little point in having t4 although some schools of thought say that t4 is used in some cells.


  • Thanks so much for replying. What I don't quite understand is why my T4 is lower now I'm taking T3. It was within the normal levels before. I didn't expect it to go up on T3 but wonder why it has gone down. Any ideas? Thanks again for your help.

    By the way I did try T4 and then when that didn't help, T4 and T3 together. The combination of T4 and T3 made me feel like I was being poisoned. So now I'm on just T3.

    Best wishes

  • Your t4 is lower because you are not taking t4 and your thyroid isn't working very well so isn't producing very much, hence the low t4 showing in your blood test. Hope that helps.

    Jo xx

  • Also it is nothing to worry about but quite natural when on t3 only.

    Jo xx

  • I agree with all of the above and think you might need a small increase in T3, as on T3 only I would expect your fT3 to be nearer to the top of the range, and your TSH supressed. However, how you are feeling is much more important than blood tests. xx

  • Thanks everyone that is very helpful. I am hoping to get a small increase in T3 at my next appointment as although vastly improved I am still a way off normal health.

    Thanks again for reassuring me.

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