Thyroid UK
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Why does TSH

Hi- I’ve been working with my doctor and endo for 9 months now. About 2 years ago TSH stopped being produced. I’ve been on thyroid therapy for about 8 years - NDT for 6 of those eight - I was on NDT 120 mg when suddenly my FT4 dropped below range and my TSH went below range. The endo insisted I go on synthroid and then they kept lowering the dose but my TSH levels never came up. I’m going to insist that my dosage is raised as I’m hypo - weight gain swelling achiness feeling blah. Currently my labs show on 150 ug synthroid

TSH 0.08 (range 0.32-5.04 mU/L)

FT4 13.9 (range 10.6-19.7 pmol/L)

FT3 3.36 (range 3.00-5.90 pmol/L)

TPO antibodies 75 <35 ( considering 8 years ago I was > 1000 - the endo says this is because my thyroid gland was s almost completely destroyed- nothing to do with gluten free/sugar free/ dairy free)

My question is why does the TSH stop signaling? Obviously im not hyper.

Thankyou for your thoughts on why TSH stops being produced


11 Replies

Because you don't need it if you are getting T4 (and/or T3) from your meds or because your pituitary or hypothalamus aren't working according to the textbook. TSH is not a thyroid hormone.

It's usual to have low TSH and low Free T4 when taking NDT or T3. As long as free t3 is in range, that's fine.

I would want to see free T3 higher - at least 4.9 (in top third of range) and when on levo free T4 should be in top quarter of range (at least 17.4). You are undermedicated regardless of your TSH.

Dropping your meds won't necessarily make your pituitary and hypothalamus behave the way the endo wants them to.

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You want TSH as low as possible. It's the message from pituitary to tell thyroid to work, it should be turned off as you are on Thyroid hormone replacement

When on NDT or T3 the TSH is very often completely suppressed

The important things to look at are FT4 and FT3. Both are on low side

FT4 is often low on NDT, but FT3 should be higher. You need dose increase

All thyroid tests should be done as early as possible in morning and fasting and don't take NDT in the 12 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results

What about levels of vitamin D, folate, ferritin and B12. These need testing, very often too low with Hashimoto's and need supplementing

Post results and ranges on new post when you get them


Micronutrient testing for B12, folate, D are all high end. I do these once a year as I have to pay. Iron is good - tests are 6 months old though. I supplement well.

Yes even after about 9 months on Synthroid the TSH did not signal... no T3 added..

I’m back on 175 ug now and will add in T3

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If TSH has been suppressed it doesn't always recover.

Which is why Endo's shouldn't mess about with dose


Agreed- but if I’m suppressed to zero TSH is that dangerous? I’ve read articles stating lower end is good but to have zero which it is on a dose I feel ok on ... Is that dangerous? I can’t find any articles on this thing support my case- being hypo sucks I can barely move - exhausted -


Dr Toft, past president of the British Thyroid Association and leading endocrinologist, 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 articles from Thyroid UK email print it and highlight question 6 to show your doctor

please email Dionne:

Prof Toft - article just published now saying T3 is likely essential for many, otherwise we have to have high FT4 and suppressed TSH


Yes but my TSH is below reference range like non existent


Hi Slow dragon I have been on synthroid for 9 months now - those were the latest results- as shown my FT3 and FT4 are low and TSH is suppressed. I’m wondering if there is more going on ie adrenal issues? The doctor wished to lower my dose to 125 ug but I refused... thanks for any input


Have you had vitamin D, folate, ferritin, and B12 tested.

These need to be optimal, not just in range

Do you have Hashimoto's

Are you strictly gluten free


Yes I get injections for B - ferritin is good I supplement with D and yes I have Hashimotos.


Oh and have been gluten free paleo diet for 10 years

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