Thyroid UK
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Does anyone know why Levo. suppresses TSH but does not raise T4 and T3


Just got my new results after G.P. told me in December to reduce my levo. from 100/125mcg. alternately to 100mcg. daily.

TSH 0.46 range 0.35 - 4.7

T4 12 range 7.8 - 21

T3 not done

Dec. 2014

TSH 0.11

T4 13

Have been taking levo. for four years and when I was first diagnosed my

TSH was 8.9 and T4 10

I do not have the ranges but I remember the Doctor saying I was right at the bottom of the range for T4 and when I had the test at a later date it said on the lab. report the ranges had changed since then to the current ranges.

My T4 has never been more that 14 and T3 never more than 4.4 range 3.8 - 6.0

In my post last week I was advised to add T3 but I have decided to get my T3 tested privately next week first.

I do not understand why although the levo. reduces my TSH my T4 and T3 does not raise much.

Does it mean I need more Levo. need T3 adding or need NDT.

Any advice gratefully received

Thank you browny

9 Replies

Browny, Low FT4 means more Levothyroxine is needed, even if TSH isalready low or suppressed. Reducing Levothyroxine usually reduces FT4 and raises TSH. Very low doses of Levothyroxine can suppress TSH in some people. Low FT4 makes it is difficult to convert sufficient T4 to T3. If TSH is low, FT4 is high and FT3 low this usually means there is a conversion issue and the addition of T3 can be beneficial.

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Many thanks Clutter for your reply,

I have read if you have high T4 but low T3 it means you have a conversion issue as you have said but does a low T4 and low T3 like I have also mean a conversion issue also. Sorry if I sound a bit thick but I still do not fully understand it all. So in your opinion what is the best meds. for me.

Thank you


Browny, It's low TSH, high FT4 and low FT3 which indicate a conversion issue. Low FT4 indicates undermedication. You could increase T4 to see whether your FT4 and FT3 improve or add some T3 which will improve FT3. Increasing either will lower your TSH and adding T3 will probably lower your FT4 which won't matter because you won't need to convert when taking direct T3. If your FT4 and FT3 have always been low I'd plump for some T3.


Great thanks Clutter,

thinks it is about time to add T3

Thanks for the advice browny

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Is it that easy? T3 is not a recommended treatment but docs may prescribe it. Many do not or only rarely as per endo I saw .Not cost he said .Really?


Hi Treepie,

not sure what you mean, do you mean the Doctors and Endos. say T3 is not a recommended treatment?

I was going to buy my own like many other people do.



"Best practice" provided by the RCP's guidance" The diagnosis and management of primary hypothyroidism" developed on behalf of organisations such as British Thyroid Association,British Thyroid Foundation and Society for Endocrinology and endorsed by RCGP states " overwealming evidence supports the use of thyroxinet4 alone. The guidance does not recommend prescribing additionalT3 hormone in any presently available form.

As we can see on this site some docs do prescribe T3 but many ,like you, have to buy your own.


Treepie, I've read the document you refer to.

I'll take it seriously when they publish it with the authors names and put references on it.

As it stands at the moment it could have been written by anyone based on nothing more than what way the wind was blowing or what the tea leaves said in the morning.


Bean, you forget that the Royal Colleges are comprised of Gods . Gods do not need to give references to justify their powers. But in this instance they prefer to remain anonymous ,which must be a godly right.


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