Thyroid UK
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Will taking synthetic t3 alongside synthetic t4 suppress t4 storage?

Will taking synthetic t3 alongside synthetic t4 suppress t4 storage?

If t4 is lower when taking (NDT) natural thyroid hormone because it contains the active t3, therefore needing less stored t4 for conversion to t3, would taking a combination of synthetic thyroxine/t4 and t3 do the same?

I read many folks who need and feel better on synthetic t4/t3 combo. I know folks who are fine on t4 only.

I also read advice across different forums about getting t4 in upper-mid range even on natural (NDT) desiccated thyroid replacement, and topping up NDT regime with t4 if t4 storage levels are very low.?

Even STTM, staunch anti-synthetic t4 campaigners, advocate mid/high t4 in spite of advice that NDT suppresses t4 levels?

What sort of t4 levels can folks expect on t3 only ?

I'm asking because...

If I top up my levo with t3 and not tell my gp will that suppress my t4 storage build up, in turn, skewing my blood test results to a lower t4, higher t3 and (presumably) lowered tsh ? Whilst I'm twitching like a junky, I am worried about being stuck on the t3 top up without properly giving the t4 a try and letting the levels build to a true picture where they, or my doc thinks they should be on t4 only? Thing is I'm on my knees already, on the lowered dose of hormones while he does his thing in his own time. I relapsed a couple of times into taking tiny t3 top ups which vastly improved my symptoms. But suspect I'm just messing up a stable reading to work from.

My gp along with many others thinks my currently slightly-elevated-over-the range TSH isn't too bad a thing. Don't know about you guys but the last time I was slightly elevated I was near death! My original logic was to stick with the programme to reach a true picture of ranges on t4 establishing a baseline to work from towards healthier me and ranges without peeing my doc off in case I need help for other stuff along the way. I will at the very least get my labs done at four weeks and return. Advice on readjusting dose seems to range between four weeks min and eight weeks max to read properly circulating levels...with additional care for adrenal and or heart probs. Thanks for reading and answers you feel so inclined.

And here's a picture of a cat to make my post more interesting x

6 Replies


Results aren't skewed by adding T3 but they are different. FT4 needs to be in the upper range when on Levothyroxine only in order to convert to T3. When taking T3 direct, either via Liothyronine+Levothyroxine or T3 in NDT, FT4 doesn't need to be so high because you are taking T3 and FT4 often drops lower in range, sometimes even below range. Most people taking T3 in any form will be comfortable when FT3 is in the upper third of range. If FT3 is good it doesn't matter that FT4 is low.

I think blood testing before 6-8 weeks after a change of med or dose is premature. I found FT3 levels responded more slowly than TSH and FT4.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

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OK. Thanks very much Clutter x


When on any form of T3, the body will only hang on to as much T4 as it needs, no matter how much T4 you take.

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Thanks Greygoose. So, I think I will h

Just have to crawl through this till and stop fiddling, and see what next blood results. Becoming very hypo now, symptomatically anyway. STTM advocate 2 weekly rises until a certain dose then hold for four before blood tests. Unless they have changed that policy.


Yes, well, that's STTM, this is the real world.


Lol x

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