This website is dedicated to the millions of thyroid patients who are being ignored and left to suffer unnecessarily, and to healthcare practitioners, who want to better serve those patients.

Thyroid Hormone Information

Thyroid hormone is needed for energy production by every cell of the body. If the cells are not getting enough hormone, then nothing in the body works properly.  The same effect is suffered by all other glands, including the adrenals (adrenal glands), which secrete an important hormone called cortisol. Although thyroid hormone is referred to in the singular, sometimes referred to as just thyroid, there are two main hormones secreted by the thyroid, T4 and T3, as well as small amounts of T2, T1, T0 and Calcitonin. The thyroid mostly secretes T4, which functions as a storage hormone and is therefore inactive, and a much smaller amount of T3, which is the active hormone. These circulate in the bloodstream bound to carriers. The very small amounts of each hormone, free and ready for use in the body, are: free T4 and free T3. This is what is measured in the thyroid function test.

Both free T4 and T3 in the blood enter the cells. T3 goes straight to the nucleus of the cell receptors and binds there, a bit like a key fitting in a lock. Once this key is turned all sorts of reactions begin. T4 is changed or converted into T3 by the deiodinase enzymes. Some of this T3 also goes to the cell receptors to be used by the cells, the remainder goes out of the cell into the circulation. This conversion process may not work very well, even with the person’s own natural T4. In people treated with levothyroxine, a synthetic form of T4, the level of T3 tends to be lower than it would be naturally. Therefore, synthetic T3 is also given, although often not enough, and blood test results of people on combination therapy are never going to look like those of healthy people.

TSH is the signal sent by the brain to the thyroid to produce more hormone. If the brain thinks the level of hormone is too low, the TSH rises, as in hypOthyroidism. If however, the brain thinks that the level of hormone is too high, then the TSH goes right down, as in hypERthyroidism. In healthy people the TSH response varies from person to person, as the brain and the body work together. The response by the thyroid may become blunted as you become more hypothyroid. Please note: the low TSH of hypERthyroidism, the speeded up and less common form of illness, is not to be confused with the low TSH produced by adequate thyroid hormone replacement. Unfortunately, endocrinologists frequently confuse the two! Also, if your TSH is anywhere in a very wide reference range, that is deemed okay by most endocrinologists, as many of us have experienced. They are treating a test, not a patient. TSH does not correspond with symptoms. You can have a very high one but not be that unwell. It can be within the reference range, but yet a person can be very ill.

There is one more hormone that is sometimes measured (rarely by the NHS), and this is called reverse T3 or rT3. This is produced by one of the deiodinase enzymes, referred to above, from T4. It inactivates the nuclear receptor and acts as a kind of valve to prevent too much active T3 getting to the nucleus. People taking T4 orally, particularly levo, may make too much rT3, which shows up as poor conversion in a blood test. Poor conversion is when you have a low amount of T3 relative to T4 – this is why some endos give T3, although not enough usually. Excess rT3 can cause hormone resistance as it blocks the receptors at the nucleus. If you are very ill you may also produce a lot of rT3. Note that NDT also contains T4.


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Previous comments

Dear Sheila , I have just told they are no longer selling Erfa Thyroid,I tried some Nature Throid but that has left me wracked with pain .
I need to find some more Erfa , the Nature Throid took too long to get ,my Bank put all sorts of problems in the way .
Any ideas please . I have so many Auto Immune problems, normal prescription medications upset me .
Kindest Regards Barrie .

barrie smith,

I wonder at some of the claims here. You say, the levels on combination teraphy will never be like those of healthy people. Do you mean that as a negative? We hypo don’t WANT the levels of a healthy person. A healthy person typically has a TSH around 1,5, ft4 under midrange, at 40% of range, ft3 around midrange. You can see results from 3800 euthyroid people here, I have written about this on my blog. But us hypothyroid can’t aim for the levels of healthy people. We need higher levels than them, as we cannot produce more as needed. But our levels need not be the same on all medications, depending on whether we can convert or not. So optimal levels on T4 mono teraphy and combination teraphy needs to be different.

Also, the role of Rt3 has been widely misunderstood. I also write about this. But you can also find info on Thyroid Patients Canada. They have several articles on it. It’s actually not Rt3 that blocks ft3. It does not create a valve or anything else. It’s deodinase type 3 that does the blocking. Rt3 has 1% affinity for the ft3 receptors. That is, it does not adhere. Also, Rt3 does not go towards the cell nucleus. It’s STTM that has perpetuated these misunderstandings around Rt3, based on Kent Holtorf ‘s misunderstandings.