Calculating T4 and T3

[Noelnoel]

Morning all

It’s been talked about many times on here regarding T4 equivalent to T3. If it’s possible to know that - and I’m not sure it is. At least not accurately anyway - what’s the T4 equivalent of 15mcg of T3 please

Thanks

[helvella Administrator Thyroid UK]

I have tried to explain why there is no possibility of a conversion factor in my blog, here:

helvella - How much more potent is T3?

Introduction

The potency of T3 (as a multiple of T4) is the source of much confusion.

You can find claims of T3 being anything from fifteen times as potent, down to being around twice as potent. And many of these claims are not based on good science.

helvella.blogspot.com/p/hel...

It is complex. I have tried to explain how I see it.

[Noelnoel in reply to helvella]

Thank you helvella and greygosose, it’s as I thought, not at all reliable then

[greygoose]

I don't see how you can compare potency when you are talking about two different hormones that do different things. It's like comparing apples and oranges, or bananas and grapes. They are all fruit, but different. What's more, it depends on the individual, how much of their dose of each they absorb and how well the convert, what they had for breakfast, etc. If you are changing from one to the other you can only make a rough guess and adjust from there once you're taking it.

[Noelnoel in reply to greygoose]

Thank you helvella and greygosose, it’s as I thought, not at all reliable then

[greygoose in reply to Noelnoel]

Not at all, no.

[jimh111]

In terms of suppressing TSH T3 is 3x as potent as T4 in tablet form. It is 4 or 5 tomes as potent in the blood but this doesn't allow for different absorption rates and half lives.