Why would I need less thyroxine after 30 years ... - Thyroid UK

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Why would I need less thyroxine after 30 years on same dose?


I've been on 150 mcg thyroxine for around 30 years. My reading over the years have been within range then went down to 0.01 but as I felt absolutely fine my long term doctor said it was okay to stay on that dose. Now another doc has said I should reduce the dose to 125mcg which I eventually agreed to. After 3 months my blook test had TSH of 0.03 and doc called me saying I should reduce to 100mcg to get within range. I was actually going to say I wanted to go back to 150 mcg as I had started to feel a little colder and slow.

What I want to know is why my readings would start to decrease. I had RAI nearly 40 years ago but is there any possibility of any residual thyroid making a comeback?

14 Replies


It's not all about TSH and I do wish doctors could understand this. TSH is not a thyroid hormone, it's a pituitary hormone. The pituitary checks to see if there is enough thyroid hormone, if not it sends a message to the thyroid to produce some. That message is TSH (Thyroid Stimulating Hormone). In this case TSH will be high. If there is enough hormone - and this happens if you take any replacement hormone - then there's no need for the pituitary to send the message to the thyroid so TSH remains low.

So it's FT4 and FT3 that are important. FT4 to ensure you are getting enough replacement hormone, and FT3 to ensure that the T4 (a storage hormone) is being converted well enough to T3 which is the active hormone that every cell in our bodies need.

If your GP wants to reduce your dose again, or if you feel you need an increase, ask for FT4 and FT3 to be tested. You can only be overmedicated if FT3 is above range.

Check out the following thyroiduk.org/tuk/about_the... > Treatment Options

According to the BMA's booklet, "Understanding Thyroid Disorders", many people do not feel well unless their levels are at the bottom of the TSH range or below and at the top of the FT4 range or a little above.

The booklet is written by Dr Anthony Toft, past president of the British Thyroid Association and leading endocrinologist. It's published by the British Medical Association for patients. Available on Amazon and from pharmacies for £4.95 and might be worth buying to highlight the appropriate part and show your doctor. However, I don't know if this is in the current edition as it has been reprinted a few times.

Also -

Dr Toft states in Pulse Magazine, "The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l. Most patients will feel well in that circumstance.

But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

You can obtain a copy of the article by emailing Dionne at tukadmin@thyroiduk.org print it and highlight question 6 to show your doctor.

Thanks. I'll try and get a copy of Dr Toft's findings but as this was only a phone consult I was able to suggest to doc that he looked at Toft's work seeing as he said he was interested in thyroid probs. He was quite happy to keep appointment I'd made for next week but I'll nip over to the surgery to get a print out and see if it was for full bloods. Thanks again!

Hidden in reply to SeasideSusie

I just looked up the booklet and in the US it's available from amazon.com for $12.95 Planning to order. Thanks, Susie, for the particulars. Will add to my growing 'thyroid arsenal.'

Catseyes235 in reply to Hidden

Thanks . . Will check!


The last thing doctors should do, especially if you've been stable on a dose for years is to adjust our dose according to the TSH alone.

I agree with SeasideSusie and I think our instinct kicks in when we doubt what the doctor/endo is telling us.

Thyroid hormones FT4 and FT3 are more informative

I 'm afraid that age does eventually wither and the years condemn! That is, as you get older physical activity tends to fall and thyroid needs can decline. However, whatever the TSH value, I wouldn't go below 125 for T4 and return to 150 if it harms. The thyroxine needs surely haven't dropped by 50% for 100 to be OK. The TSH is simply a reminder of past doses and is no indicator of the present.

Catseyes235 in reply to diogenes

Yes just from those readings I should be sweating, shaky, running round like a headless chicken and thin as a whippet . (I wish!) !


Essential to test your vitamin D, folate, B12 and ferritin

If dose has been reduced, often vitamin levels drop, then TSH stays low

They should not dose just according to TSH......its latest obsession to bring TSH up "within normal range" but if we are on Thyroid hormone replacement we often need very low TSH

For full Thyroid evaluation you need TSH, FT4, TT4, FT3 plus TPO and TG thyroid antibodies. Plus vitamin D, folate, ferritin and B12.

Essential to test, FT3 and FT4, plus vitamins

Private tests are available. Thousands on here forced to do this as NHS often refuses to test FT3 or antibodies


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should ideally be done as early as possible in morning and fasting.

If on Levothyroxine, don't take in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip, GP will be unaware)

About 90% of all hypothyroidism in Uk is due to Hashimoto's. Low vitamins are especially common with Hashimoto's. Food intolerances too, especially gluten. So it's important to get tested.

Thanks I'll see if get full bloods . . they usually do but receptionist printed off request and didn't study what was requested . T3 has been fine previously with TSH 0.01. I take lots of supplements as mentioned. Funny that doc is worried about future heart probs and osteoporosis when bone density is okay and resting heart rate is good. Surely should be asking if I'm getting palpitations , sweats etc!? Seeing my old doc 2 days after so should be interesting to get his take as he agrees with me!

SlowDragonAdministrator in reply to Catseyes235

If they still want to reduce dose, you can refuse. The GP is there to advise and you are an active participant in your own care

Point out that if they reduce your dose further, you will have no energy to exercise, get of sofa etc.

Exercise is the prime way to keep bones healthy. Not being stuck on sofa in state of exhaustion

I'm may give it a go for a few weeks from June after I have finished an invigilating job just to see what happens. Don't worry I fight my corner and it was nice to see others have such a low TSH reading and feel fine too. I've been way way at the other end of scale . . next stop comatose - It's good my regular doctor supports my viewpoint. Hope you're well!


same happened to me yesterday.

my TSH was allways around 0.05-0.01 and now my GP is up in arms for me to get a higher TSH!!

after years of explaining to me how irrelevant the TSH and ft4 is, if taken Tertroxin (20mcg of t3) !!

he also prepared me for the withdraw of t3 as it is ever so bad for the heart.......now it is......I wonder, that he was trying to kill me , when subscript was 40mcg of t3????

I live in Australia and there was never a problem for the t3...

I would say, don't go the 100mcg way....rather top it up to the 150 again.


Catseyes235 in reply to christa1

Thanks for that. Thing is I never took T3. I did ask what the chances were of having it and he said slim! Luckily I'm seeing my long time doc who is a senior partner 2 days after seeing the overzealous one. May start some debate within the surgery which may be no bad thing!! Understanding the thyroid with its feedback loops and logarithmic TSH scales etc is confusing enough without the lack of understanding in the medical profession. Got enough else going on in my old age without going back to thyroid probs!

Don't reduce it further Catseyes. In 2012 my new GP started reducing my 150mcg levo because of my low TSH and high FT4. I am sure this was when I started getting heartburn a few times a week. She reduced it again and I got an awful pain in the gall bladder area (just as I did four months after my sub-total thyroidectomy back in 1985, which led to a scan showing no gallstones), had a gastroscopy where Barrett's Oesophagus was discovered and now I am on PPIs forever.

My GP eventually reduced the levo to 75mcg and my stomach became worse and I had urticaria and angioedema. I saw an endo through my work's private insurance and he put me back up to 100mcg, saying I could probably take a bit more. The endo wrote to my GP saying to titrate and as long as the TSH was measurable it was ok, but she doesn't seem to understand what he meant by measurable.

I am sure the thyroidectomy is responsible for all my digestive issues (and I fought against having it) and maybe I didn't have the Barrett's until my levo was reduced. I only wish I had known about this excellent forum in 2012.

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