Thyroid UK
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Lower TSH

I was only diagnosed as hypothyroid 8 weeks ago and have been on levo for 7 weeks. I am getting the results of my first bloods since being on levo, on Friday. Trying to inform myself, so apologies if this is a basic question.

My question is this: If low FT3 causes hypo symptoms, how is it possible that TSH can be reduced by levo, but your FT3 does not increase? I thought that your body only reduces TSH production if more FT3 is being produced? If my TSH levels have gone down into normal range on Friday, why would this be? I don't feel any better (except for an initial spike in the first few days where I felt really, really well), so I'm guessing that my body still isn't using the FT3.

Is it not only FT3 that can switch TSH off? I really hopes this makes sense. I'm getting very confused!

7 Replies

TSH is the messenger for your body to make T4, T4 is converted into T3. When you get your blood tested they will check FT4 and TSH and sometimes FT3.

If your TSH is high it means your body is asking really loudly to make T4. If the body fails to do so we can add T4 with medication (Levo). We take the medicine and our body gets more T4 so the TSH will get lower. You want it to be around 1.0, "in range" is not good enough.

Your FT4 will get higher, you want it to be in the upper range.

Your FT3 will also get higher, if not then there could be a problem in converting T4 in T3, in that case you can try to add T3.

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Hi Meds, Flower gave a good explanation that TSH recognizes T4 which is what your own thyroid is supposed to produce in the amounts you need for your rate of metabolism. This article might help you understand what happens after that. And, yes, your adrenal glands can also switch your TSH downward if they are too weak to keep up with thyroid hormone.

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Any thyroxine can suppress or reduce your TSH, that's why measuring it is less than useless!!


It is quite complicated but regarding your first blood test after

being on levo, make the appointment as early as possible and don't take levo until afterwards. You take levo with 1 glass of water and don't eat for around 1 hour.

Always get a print-out of your blood test results with the ranges, for your own records and so that you can post for information. If GP hasn't tested B12, Vit D, iron, ferritin and folate ask for these to be done as we are usually deficient.

We get prescribed levothyroxine as that is what the Guidelines of the British Thyroid Assocation state is the only one to be prescribed by GPs. Despite the use of natural dessicated thyroid hormones being in use successfully since around 1892 in various forms, and it contains all of the hormones our body would naturally produce, T4,T3, T2, and T1 plus calcitonin doctors are afraid to go outside the guidelines and, of course, levo is approx £1.50 per month.

Lots do well on levo but some of us don't.

Levothyroxine should convert to sufficient T3 which is the active hormone our Receptor cells require for us to function. They don't usually test the T3 if TSH is 'in range'. Its also a more expensive blood test, I believe. To assist levothyroxine to convert taking some Vitamin C at the same time can help. Other medications/supplements have to be taken 4 hours apart from levo.

There are other topics on the left-hand side of the above link which may be helpful.


So does the pituitary gland detect the levels of T4 circulating in the blood, and then tell itself to stop producing TSH if it detects enough T4?

I still don't understand why the TSH levels drop. How does the pituitary know to stop producing TSH, if the cells are not converting from T4 to T3, for example? Does it just detect T4, irrespective of whether that T4 is being useful?


This is why the TSH test is such a poor indicator of thyroid status.


The doctors and endocrinologists should have more knowledge of the clinical symptoms (which they appear to be completely unaware of) and the TSH is not necessarily a good guide in our wellbeing. As noted by eeng above. Some people's TSH doesn't rise sufficiently for medication which is deemed the 'Exquisite' point for diagnosis even though they have plenty symptoms.


The TSH level is not a measure of thyroid hormone levels--only the free T4 and free T3 are. TSH is a measure of how much the hypothalamic-pituitary system is attempting to stimulate the thyroid gland. A "normal" TSH tells us only that the person doesn't have failure of the thyroid gland. It does not tell us that they have sufficient levels of thyroid

hormone. A normal TSH does not "rule out" hypothyroidism.

The very best way to know that you are on optimum thyroid hormones, is how we feel. If we are back to normal health or still struggling.


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