Hi Elbeth - because some people do not get well with natural thyroid.
Yes T4/T3 or natural thyroid is the first choice medication but there are many reasons why some people can never get well on natural thyroid. I am one of these and there are many more people in this category.
My website
http://recoveringwithT3.com has a lot of information on this and why thyroid blood tests can sometimes not reveal what is happening in our cells.
Some important information for you to consider is:
1. T3 is the biologically active thyroid hormone. The others T3,T2,T1 have some effect - but very little. T3 is ten times more effective than T4 for example.
2. For someone to get well with thyroid hormone they need only to have enough T3 in their cells and have that T3 active there. They need no T4. I have no T4 in my body - yet I am well!
3. The way the thyroid hormones work is that enough T3 has to enter the cells. Within the cells enough T3 has to bind to receptors on the mitochondria and in the cell nuclei. The T3 makes the mitochondria produce ATP energy (if there is enough glucose). The T3 makes the nucleus produce the right proteins.
4. Blood tests only measure thyroid hormones in the blood - they cannot see what is happening in the cells - at all!!!!
5. Many things can go wrong between thyroid hormones being in the blood and going inside the cells and making the insides of the cells work right. If it goes wrong we cannot see this in blood tests at all!!!!
6. My 'Recovering with T3' book explains how all this works, what can go wrong and how it can be fixed.
7. My background is science and I approached all of this with a scientific method and with medical references. The information in my book is backed up with medical science.
8. Doctors do not know most of this. They think thyroid blood tests tell them what is happening in the body - they don't for some people.
9. For some people the problems they have cause what I call 'impaired cellular response to thyroid hormone' - which means there may be thyroid hormone in the blood and even in the cells but it doesn't work right. To fix this much more T3 need to be there and natural thyroid cannot be made to work.
10. Only some people need T3 on its own. However, for them it gives them back their health - it did for me and it has for thousands of others.
I hope this is clear - it is not a myth - it is a fact.
Best wishes,
Paul