T4 to T3 Conversion

I have just published a new blog post. This is an interesting one as it shows the linkage between TSH and FT4 to FT3 conversion.

I don't mention this in the blog post but this relationship is critical to why CT3M is needed (I say more about that in The CT3M Handook and in another blog post which I will release soon).

You can find this latest blog post on my book Facebook page: facebook.com/recoveringwitht3

For many of you if you 'like' the above page then you may well get automatic notifications of new postings there - this means you'll know about changes on my website or about book releases etc.

Best wishes,


p.s. for those without Facebook please see the blog post on:


43 Replies

  • Hi Paul, that was a really interesting and illuminating read, thank you. I note the C3TM method is not appropriate if your adrenals are okay or if you have a problem with HPA axis. Had adrenals checked in April 2013 and they were okay except for slightly high night time levels of 4.2 (1.0-3.0) explanation - might be suggestive of malfunctioning of the hypothalmic adrenal axis feedback system.

    I am on T4/T3 combo and seem to be in the position described in your blog. If T3 lowers your TSH how would you manage to keep it in range without lowering your meds. My TSH is 0.13 (0.35-5-5) with low T4 and T3 just below middle range.

    Is this all explained in your new book.

    Thanks, Jan

  • You don't attempt to keep FT3 in range because taking T3 is always likely to raise FT3 to the top or beyond the range. Blood tests cannot be used to manage T4/T3 treatment, NDT treatment or T3 treatment.

    You say your adrenals were OK but for this to be true this would have had to be an adrenal saliva test with:

    1. sample 1 at the top of the reference range.

    2. sample 2 in the upper quartile

    3. sample 3 mid range

    4. sample 4 bottom of the range

    - was this true?

    TSH can also become mal adjusted to a new low set point and then it becomes useless - better to use FT4 and FT3 alone and symptoms and signs or just to go by symptoms and signs.

    Good luck Jan.


  • Thanks Paul, had Genova Diagnostics Saliva test done these were the readings:-

    Sample 1 - 20.4 (12-22), Sample 2 - 6.5 (5.0-9.0), Sample 3 - 6.8 - (3.0-7.0) and Sample 4 - 4.2 (1.0 - 3.0).

    DHEA (am) 0.33 (0.10-0.50), (pm) 0.46 (0.4-2.0)

    Lab said normal adaptation, except for night which was explained above.

    They don't correlate perfectly, do you think they need some help.

    Many thanks, Jan

  • They don't correlate perfectly but these aren't bad results. I might use an adaptogen like PS (phosphatidyl serine) to calm the adrenals a little at night and perhaps a little ashwaghanda or Holy Basil in the daytime to support the adrenals but I wouldn't be looking at doing anything significant. Good results overall.

  • Bless you and thanks, one less thing to worry about. Will give your suggestions a try.

  • hi hope you can help I have a readon of 14.5 pmo/l for my free T4 test and a reading of 1.87mIU/L for the TSH is this bad

  • Hi there. My real focus is on those people for who begin using T3 only therapy.

    I don't work with general thyroid issues really.

    Your test results really do require FT3 at least and ideally rT3 also.

    The two results you have are the least useful of them all. They are probably both in range and could be quite ok if FT3 and rT3 are good and your symptoms are caused by something else other than thyroid. But TSH and FT4 are simply not sufficient on there own.

    I'd put up a more comprehensive post somewhere on this site so that others can see your medical history, symptoms and any other test results. There are a lot of excellent people here who would probably have some insight for you.

    Good luck.


  • Hi Paul

    Am interested in your comment about blood tests here.

    I take NDT and have managed to get the doc not to panic about the very, very low TSH which has allowed me not to reduce meds as the Endo wanted. But I was still under the impression from various posts I've seen on here that the level of T3 had to be in range and that it was dangerous for it to be above top of range.

    I would be very happy if this is not the case as I still feel under medicated and would like to try an increase but have been put off by fears over high T3.

    Do you just assess T3 requirement on signs and symptoms? Do people actually have over range T3 on blood tests without dire consequences?

  • Keeping values in the reference range are not always helpful for some patients. An extreme example would be patients that can only get well on T3. Typical lab tests then show FT3 well above the reference range, near zero T4 and near zero TSH. These people are perfectly fine like this. Blood tests do not reflect the actual cellular activity of thyroid hormone for many patients - I am one such patient like this.

    Anyway, for the original poster I was suggesting getting FT3 high in the range not necessarily above it.

    It is not dangerous for some people to have FT3 above range. For others they are better when it is in range. Symptoms and signs and blood tests of FT3 and FT4 can be used together to manage dosage and ensure that an individual feels well, has no heart rate, blood pressure or any hyperthyroid symptoms as thyroid hormone is increased. If the person is well on a high FT3 but sick on a mid range one then isn't better to have them well?

    This is what my book 'Recovering with T3' talks about frequently. Doctors should be treating the individual not just the blood test results.

    Best wishes,


  • Hi Paul

    I know this is off topic from your main post, but following on from what you said about some people being better above the T3 range (myself), why is it necessary to have bloods at GPs, when possibly they mean nothing. I am on T3 only and I am having to reduce it before I get tested, otherwise I would be above the range and my nhs prescription would be reduced. Do you think the range should be changed?

  • It depends on what meds people are on. On T3 only I actually think there is little point apart from a very occasional check to ensure that nothing very peculiar is going on that might suggest thyroid or pituitary misbehaviour. My own doctor has to do a once a year test to meet the needs of the health authority and assure funding of some kind. It is a tick in the box test as she and I both know the results are not useful.

    The FT3 range for T3 treatment is so crazily variable that it would be of no use.

    I know people on 150 mcg of T3 a day and FT3 that is double the top of the reference range so the FT3 range is really of no value in T3 treatment.

    Best wishes,


  • Thanks for taking the time to reply Paul.

  • No problemo. I used to post here a lot and know a lot of folks here. Lynn Mynott has kindly put my book on the TUK website also. It is good to do some work in the UK only sometimes.

  • Really interesting article - and I had read Paul's book a number of times - I highly recommend it.

    I am seeing my GP tomorrow as I have very much gone backwards in health terms and I want their support in trying CT3M as a protocol to heal adrenals and hopefully reduce medication doses overall. I was taking all of my T3 at night (40mcg) which made me sleep like a log for months but now I am awake half of the night so something has gone awry.

    My first key job will be to get GP to agree to run a panel of blood tests (TSH, T3,T4, Ferritin and D3 - I don't think they will run any other tests on the NHS but anyone knows better please tell me . I have ordered private reverse T3 test and want to bring that along in the hope they will pop some blood in there for me while they are at it!!

    Saliva tests have improved a bit over the years - morning and night time sample in range but two daytime samples marginally below range. DHEA always been below bottom of range. From reading all the posts I think the major obstacle is getting GPs to accept the adrenal part of the thyroid puzzle - they seem to shy away from it so I will be taking Pauls CT3M article with me to show GP.

    Final comment- from what I understand T3 meds are a lot more expensive than T4 meds, so you would imagine they would be interested in exploring the CT3M protocol running some studies to see if that reduces overall prescription costs or am I missing something here??

  • You would imagine that they would yes. But most aren't even aware of CT3M. Pity you don't have the article I'm writing at the moment to take with you. It is the last post I'll do before the CT3M Handbook comes out. It says in a nutshell why CT3M is a tool that doctors should be considering in cases of thyroid patients with some partial adrenal insufficiency. It won't be finished for a few days yet though.

  • Hi Paul that is shame it wont be ready in time but it sounds like a fantastic article and one that a lot of people will want to read. will you be posting it onto your web site?

  • Yes and as usual I'll probably blog here.

  • Hi Paul

    Just to let you know I had a great appointment with my GP today and talked to them about the problems I am experiencing and how I very much wanted a full bank of tests done to see where I was and wanted to try CT3M to see if that helped.

    They were hugely receptive and supportive! They said it made absolute sense to space out and carefully time dosage of thyroid meds as the body doesn't just dump a load of hormones in one output. They were interested in your CT3M approach/info I passed on. They said they were hoping more studies would be done as they have worked with so many hypo patients who struggle with the one size fits all/narrow approach currently being adopted.

    Just wanted to let you know as it was great to have professional and experienced GP be so open to new information and your CT3M approach.


  • Wow!!!! I don't often hear that kind of response - that's great Lizanne!

  • Hi Paul - just to let you know outcome. GP ran a load of tests, all came back in normal range apart from TSH (no surprise there that it was so low). I also had reverse T3 test done at the same time and that came back normal range too - which I was a bit upset about as I was hoping it would prove I was not converting properly, I knew I had adrenal problems from tests and taking my T3 helped. Really puzzled now as to what is wrong if its not reverse T3 issue so I am going to go back and read your book again (every time I read it I find something new I missed before!).

  • I'd have to see both the T3 and the reverse T3 numbers and the units they are in and the reference ranges. Please remind me what thyroid meds and doses you are on.

  • Hi Paul I have all the test results if you are happy to look at them? I am on 125mcg of T4 and 40mcg of T3 but now reducing T4 to 100 mcg

  • I will but won't be able to today. You can post them though.

  • Hi Paul - thanks I have posted latest results here. I was convinced I had a reverse T3 issue but tests say normal, Still trying resolve symptoms especially hair loss. I am definitely sticking with CT3M as my adrenals are still very weak but will look at other avenues - maybe need more B12 etc..

    Latest test results

    Coeliac test - result normal

    Vit D 85.4(80-150)

    Calcium 2.39 (2.1-2.55)

    Vit B12 462(187-883)

    Folate 11.1 (3.1-20.5)

    TSH 0.02(0.35-4.94)

    Free T3 5.01 (2.63-5.7)

    Free T4 13.78 (9.01-19.05)

    Reverse T3 21.2 (9.0-35.0)

    Previous tests results have shown

    Testosterone 85 (150-600)

    DHEA 41 (65-280)

    DHEA Cortisol ratio 0.34 (1.0-4.0)

    Ferritin results over the years range between 38-85 (50-170). GP says iron level now food as latest Folate result above was in normal range.

  • Vitamin D could be higher. Suppementing with 5000 IUs especially over autumn/winter would be a good idea. B12 should be much higher so supplementing with 1000 mcg of B12 is sensible - it is not toxic.

    I need units for FT3 and rT3.

    I'm guessing they aren't in the same units. See my blog on Sherbet Lemons in the Blog sections on my website - for some even normal looking rT3 is a problem.

  • Reverse T3 21.2 range 9.0-35.0 ng/dL

    Free T3 5.01 range 2.63-5.7 pmo/L

    Is that what you mean by units- sorry if I have misunderstood. I am going to read your Sherbet lemon blog now

  • I think the FT3/rT3 ratio is a little low but as I said even if it wasn't some people can still have a problem with rT3 and FT4.

  • Thank you Paul - I need to do some more reading up on all this as it is a bit beyond me to be honest - back to the CT3M book for me I think!

  • Very interesting! I wonder if this is why I only seem to be well on T3 only. My body seems to adapt so quickly to change of dose or T4:T3 ratio that I take. Since going T3 only, I have seen fantastic improvement even before reaching my current dose. I think that was partly due to stopping all T4. Even on dessicated I never reached full health. Replacing some of the dessicated thyroid with T3 worked for a short while but then I felt worse again. I have not had that kind of relapse since going to T3 only :)

    Thanks for posting

    Carolyn x

  • Just to add, my TSH always seems to be low. When I was pregnant my TSH was just below range yet my T4 was at the bottom of the range. This was on levothyroxine only. It is interesting to note the relationship between TSH and T4 to T3 conversion.

  • It is a not well known relationship.

  • When I put up my next blog on CT3M you'll see why the conversion issue is so important. I'm also working on a video blog on why CT3M is a natural way of using thyroid hormone! :)

  • Looking forward to it!

  • It could be Carolyn it is hard to tell for sure but conversion issues of all kinds are a problem for a lot of thyroid patients. Many of us would have had very decent healthy FT3 levels before we got sick. Having low or mid range FT3 is usually a dead giveaway that someone isn't processing thyroid hormone well - even though it is 'in the reference range' :)

  • Thanks :) The GP that originally diagnosed me tested my ft3 and decided, on the basis of my blood tests, that t3 would be best for me. He didn't explain why and I knew little of such things all that time ago. Unfortunately, after a couple of years, he was told that he had to stop prescribing it and to prescribe levo instead. This is when all my 'health problems' started back up again.

    At least I'm going in the right direction now :)

  • Good guy until the cost cutters got to him!

  • That's what I suspect too. He was very apologetic. He left shortly afterwards. My current GP agreed to prescribe but was told 'No'. I'm changing surgeries out of convenience. I'm not expecting them to be any better but you never know. I'm sure they won't prescribe my 100mcg though!

  • Good luck Carolyn!

  • Thanks :)

  • This blog is really useful and timely for me Paul. Thank you for posting it it will really help me to present the argument I need to put to a new endo I'm taking my sister to see next week.

    It took me months of fighting the medical profession to get her prescribed T3 with her T4 and the agreement was that T3 was going to be gradually increased and T4 reduced. this has never happened. The only time she has shown any improvement was for about 2 weeks when they started her on 10mcg of T3 with 175mcg of thyroxine, so she morrors your description perfectly. She had been fine for 20 years on 200mcg thyroxine and then slowly and mysteriously started to become ill until she is now bed bound and has been for about two years now and ill for seven. The endo department in her local hospital have been useless and keep going by her TSH and don't even bother to mention she is taking T3 on the blood test forms.

    Recently she had a spell in hospital and the beggars reduced her T4 to 125mcg because her TSH was low - all without consulting the endo department. Not that they would have been much help. I am nearly spitting blood with the frustration at the ignorance and stupidity of it all. I will use your advice to help persuade them....wish us both luck and thanks again.

  • I doubt they'll be persuaded. Sometimes you have to take charge and do things your own way. Life's too short.

    Good luck!

  • Yes I agree. It's my sister who insists on sticking with the medical profession which adds to the frustration with trying to help her. I would have dumped them years ago - I manage my own treatment and don't consult with any of them. If only I could get her to read your book!

  • Good luck!

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