Thyroid UK
82,855 members97,885 posts

How does your body store Thyroxine ?

Hi I have no Thyroid and I am dependant on a replacement drug. The replacement meds are usually NHS Thyroxine and ideally you are advised to take your meds first thing in the morning and hour before food.

My question is when I had my thyroid my body at and educated guess would make Thyroxine and drip feed it into my body slowly through out the day. With the big input with NHS Thyroxine early am, how does my body get the replenishment it requires say at 8pm a good deal of time after I have take my dose. ?


John C

6 Replies

The dose of levothyroxine you take today will slowly diminish over some weeks. T4 (levo) is the inactive hormone and T3 is the active, which we need to function. This is an extract:-

How Does Levothyroxine Work?

The thyroid gland makes two similar (although slightly different) thyroid hormones: triiodothyronine (T3) and levothyroxine (T4). Usually, the thyroid gland produces much more T4 than T3 (however, T3 is much more active in the body than T4). The body can convert the T4 hormone into the T3 hormone as necessary. If your thyroid does not make enough thyroid hormones, there are a few different ways to increase your levels.

Some forms of thyroid replacement combine both T3 and T4 (such as natural thyroid replacement made from pig thyroids). However, because the body converts T4 into T3 as needed, most people can successfully take just T4 (such as levothyroxine). This is the most common type of thyroid replacement. Another option includes taking just T3 hormones (such as Cytomel®).

Although it is synthetic, levothyroxine is identical to the naturally occurring hormone T4.

1 like

wow thanks youve just answered a question I asked weeks ago as I didn't understand T3 and T4 thankyou


John, there is quite a process after the production of T4 whether man made as Levo or your own natural thyroid . Do you understand serum testing? It merely tells you what is in your bloodstream but T4 is quite inactive and goes into storage. It has a half life of about two weeks which means it has to build up slowly. That is usually why you start at a lower level while you find your optimal dose since it will be accumulating over the weeks and could take a month before you hit your peak. By then you may decide to raise your dose by a few mcgs. While it is stored in the liver, certain enzymes start to work on extrapolating how your body reacts to it. If you read the first two paragraphs in this paper, notice when it refers to serum that it only implies what is in your bloodstream which is a long way before it enters cellular tissue as T3.


do you think being on 75 for several months then going up to 100mcgs then after several more month going upto 125mcg is a bit too fast for your system to handle?


I'm thinking back twenty years when I started on Synthroid and was probably raised 25 mcg almost every week until I was on 100 mcg.

I really don't know for certain but I think it is far more problematic to go too slow as well. I have to say I was in a lot of pain while doing that quick increase. (Severe muscle spasms up my back) But I felt it was at least doing something to reverse other symptoms. Your body slowly begins to adapt to the increase of T4 but I would think the closer you get to what is the right amount, the quicker your body will adapt to it but really I haven't read enough to know that for certain.

What Rod mentions below may be more accurate about the T4 that isn't being used as active T3. T4 does pass through the liver for processing. What I have read is that T4 will either become free T3 (desirable) or reverse T3 (undesirable) depending on circumstances. I don't know how long it would remain as bound.


As I understand, most if the thyroid hormone in the body is held bound to proteins in the blood.

A tiny proportion of that is the free hormone available to be transported into cells.

This is what is meant by, for example, Free T4 - the T4 in the blood that is not bound to protein. Total T4 is both bound and free T4.

There is massively more bound thyroid hormone than free. As the free hormones are used, more is unbound so as to keep the free levels fairly stable.


1 like

You may also like...