Thyroid UK
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Why might my T4 be going up and T3 going down, on the same T4 dose?

Hi all,

I feel like I am going round in circles with my thyroid :-(.

I've been on 100mcg T4 for 1.5 years. My results had not changed in a year and were as follows last November:

TSH: 0.01 (0.27 - 4.2)

T4: 16.3 (12 - 22)

T3: 4.6 (3.1 - 6.8)

Then I experimented with night-time dosing over 6 weeks, but that reduced my T3 from 4.6 to 3.44, which was tested in January.

I reverted to day-time dosing and re-tested 5 weeks later. Results are now:

TSH: 0.023

T4: 18.6

T3: 3.42

Test conditions were identical. Can anyone suggest ideas why my T4 is higher than I've ever seen it, and T3 lower than ever? It seems I've lost ability to convert (not that conversion was great to begin with). And also, does anyone know how long it takes for T3 changes to be reflected in blood results?

During the last 5 weeks I also introduced 5mcg T3 daily, as prescribed by my endo, but I stopped after 6 days as I felt terrible (comatose, headaches). This was 2 weeks before my blood test above.

My vitamins are now optimal. I'm waiting on adrenal test results (cortisol, DHEA). I am so confused about what to do and I feel I am making everything worse. Should I attempt to re-introduce T3 in teeny tiny amounts? I was interested in CT3M but if I can't handle T3 that is not going to be an option. Plus need my adrenal profile before making decisions.

My endo has also put me on Metformin for fertility which I've been on for 3 weeks. Not sure if this could affect my T3?

I hate it when there are so many variables. Sorry, I've been posting a lot and probably not making much sense :-(. I feel pretty rubbish most of the time, almost too tired to keep trying to work out what I need to do to support my health!

1 Reply


Perhaps the Metformin is affecting how you absorb Levothyroxine. Do you take them at least 2 hours apart?


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