I am trying to understand how the process works when you start taking thyroid replacement. I understand that once you start taking it the

brain shuts down the remaining thyroid gland for those of us who still have some working. Does that mean we are just running on the dose of hormones we are taking? I have also been told that the hormones work with the remaining thyroid that is still functional and assists it in making t4. Does anyone know the correct answer?

26 Replies

  • I would like to know this too, Mary.

    I've read that it takes 145mcg typically to close down the bodys natural thyroid production- so if on less than this, presumably some natural self production is still possible.

    It all depends on dose and absorption efficiency in each case.

  • Thank you so much Tegz. I don't mean to sound thick, but what I am gathering from this is that unless you are taking 145mcg plus some, there is still some natural production left from the thyroid gland unless you do not have one anymore? I will read the link. thanks.

  • Yeah, as far it it goes. [but we're all different] At least it kicks debate off :)

    Not a lot of research at high level seems to get done on this whole area.

    I wonder why...Mmmm We must keep on pushing for answers...

    Lots of mony tied up I expect- [coming in I mean, for synthetics] not going out to help us!

  • I know what you mean. I once had a discussion with a pharmacutecal rep when I was in the doc's office. He told me he quit his job because he had a hard time living with himself knowing what they do and how they use people for experiements for their drugs. I asked him "then why are you back here doing it again". His reply was no matter how guilty he felt, he could not give up all that money. This was in the states by the way. Well, if that ain't an honest answer, I don't know what is.

  • No reason to think it's greatly different in the UK, Mary.

    It's all multinationals,today- especially in Pharma land.

    Interesting anecdote.

  • This hypothesis might interest you: (first link is an introduction by the late Dr John Lowe, the second the actual paper)



    The theory is that as you increase the dose of T4 the thyroid is gradually shut down - so you might feel well initially on a new dose but then the pituitary recognises there's more T4 available so switches down any natural thyroid production, so you need to take more T4 and so on, and you will therefore never reach an optimum dose until the TSH is completely suppressed and you are totally relying on exogenous T4. I don't know if anyone's ever done any actual research into this.

  • Sounds highly feasible, Jane.

    Not so much of a problem pending -if Levo was truly the same as what the body produces.

  • Wouldn't we all be on the same dose then?

  • Everyone's different!

  • No I don't think so, would depend on a lot of things, body mass, your own metabolism etc; everyone's 'normal' (set point) is different. If everyone was the same the 'normal' range would be very very narrow wouldn't it? He says you need to go beyond the point of suppression and this doesn't indicate over replacement.

  • Ok. Thanks.

  • The endocrinologist that I saw 2 years ago explained that the normal ranges quoted are based on people without thyroid problems. Whether you have a disorder or not we all have different levels of 'normality'. Levothyroxine is not the same as the hormone produced by the thyroid gland which is why we also we need to take more of it. Unfortunately many of the hypothyroid/hyperthyroid symptoms can also be attributed to other things e.g menopause etc. I take a high dose at 225mcg which appears to be ok although my T3 is currently higher than I'd like it. GP's vary in their responses to us 'thyroid sufferers'. At the end of the day they are general practitioners not experts and if we really want answers then referral to an endocrinologist is probably the answer. Having said that the one I saw sat very much 'on the fence' when I queried the use of HRT with Levothyroxine!

  • I guess what freaks me out is that I had subclinical for eight years. This is a normal t4/t3 with a high tsh of about 15-20. Just recently the t4 got a little low and my tsh shot up to 64 then in one week 94. I am only taking 25mcg of levo and in two weeks the t4 was normal and the tsh dropped to 32. I was over the moon. It has been aabout five weeks now, still on 25mcgs and I feel it has brought me down more. Will have labs back tomorrow. Just so puzzled how I could stabilize so quickly on such a low dose. I still have my thyroid so maybe I was just going into full blown hypothyroidism and the little bit of levo I am taking will do the trick.. My doc won't explain anything so I am on my own with this. I am on a financial program and cannot switch doc,s. I am anxious all the time because I don't understand it. Thank you for the input. Has your thyroid been removed? Is that why you are on such a high dose?

  • It would be good if you could get a FreeT3 test done, Mary.

    The TSH measures the pituitary response to low thyrode hormones and responds if working right, in the way yours does.

    However, whether the thyroxine is being converted to T3 [the usable form] by your body is important and a test would hopefully throw some light on this.

    With the length of time you've been struggling with it you deserve a decent response from GP by now.

  • My ft3 has always been normal. When the tsh was 94 the ft3 was normal. When my tsh came down to 32 a couple weeks ago, the ft3 went up a few points, but was still normal. Why what does that mean?

  • Normal is not always optimal. What were the readings?

  • Firts ft3 at the tsh level of 94 was 2.3(standard range at this lab is 1.8-4.6. Second ft3 with tsh dropping to 32 was 2.7 ( standard range 1.8-4.6.

  • TSH response is not linear- but for its halving, the blip on T3 doesn't look much!

    Maybe your test results will help clarify things?

  • what if you don't need to increase the dose?

  • Well, eventually this seems highly likely to be needed- by many accounts.

  • Yes, I did 'ok' for a while but then went on a very long slide.

  • what do you mean? What happened.

  • I was ok on 150mcg levo for a while,(TSH 0.06, T4 27) but looking back I don't think I was 100% well, then I started getting more and more tired and less able to cope and my T4 had dropped to around 18. I've been on doses up to 200mcg which helped but they won't allow me to have a suppressed TSH so couldn't stay on that dose (because of my age; peri-menopausal). I don't know if that hypothesis is right - It kind of made sense to me, but it does raise a lot of questions too! I'm now self-medicating with Nature-Throid and feel completely different - early days but so far so good.

  • Are you still taking levo? That is a high dose. What type of thyroid issue are you suffering from?

  • I thought as long as you had some working thyroid, the levo just gave it a boost up to the level you need to be. Confusing...

  • I suppose.

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