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Thyroid UK
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T3 only

It would be interesting to see what people think about only taking T3 or a low dose of T4 and a replacement dose of T3 (40-60mcg). Is anyone in this situation or are there any articles about it?

If T4 is just a storage mechanism for T3, the active hormone; if one is not converting T4 to T3 anyway, what's the point in taking T4 in the first place?

I'd welcome your views on this.

Thanks in advance

8 Replies

We're all different. Some people feel the need for a little T4. I'm on T3 only because that's what's best for me. And, goodness know, I've tried just about everything else. T3 only was the last resort. I've regained most of my life on that.

There is a school of thought that says the brain needs T4, or that T3 molécules are too large to pass the blood/brain barrier. But my brains works better on T3 only than it ever did when I was taking any form of T4.

So, you just have to try things and see what works for you. And it isn't necessarily what works for other people. :)


The brain needs T3 and has the most receptor cells. T4 is a pro-hormone, so I've read.


Yes, of course the brain needs T3.

My point was that taking T3, it doesn't get to the brain because the T3 molecule is too large to pass the blood/brain barrier, some people believe.

Therefore, they say, you have to take T4 - which I know is a pro-hormone - so that the T4 can get into the brain and be converted into T3 there.

But that is not my theory. I'm just saying that it is something you will often read supporting the idea that it is necessary to take T4 + T3, rather than T3 only. :)


This doctor would not prescribe levothyroxine at all. Only NDT or T3 for resistant patients. He also said that T4 could be compared to a tin of beans - which were only good if you could access the beans (or if T4 was converted to sufficient T3)


I am on T3 only now and am well. I was also good on a particular NDT. I also improved with the addition of T3 to T4.

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I prefer T4+T3 to T3 only. Poor converter but 75/100mcg T4 and 30mcg T3 works well. I think the combination is a smoother ride than T3 only, only need to dose x 2 daily which is more convenient, and I like the security of having some T4 in my system for conversion should I be unable to take T4+T3 for a few days.


According to this post, T4 does have unique properties that can't be obtained by T3: tiredthyroid.com/blog/2015/...

There are references which back it up, so it does make me wonder.

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HIFL, Perhaps T3 can fill those functions in patients unable to tolerate T4?


No, there are T4 receptors. T3 can not bind to a T4 receptor, so someone without T4 will be missing whatever T4 alone does. But it's obviously not life-threatening, or T3-only wouldn't work.


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