T3 vs T4 Read T3 five times strength T4. Als... - Thyroid UK
T3 vs T4 Read T3 five times strength T4. Also T3 ten times stronger. Which is it? Penny
Its normally about 5 times stronger than T4. If your GP gives you 10mcg's T3 he/she will normally reduce your T4 by 50mcg's.
Maybe Rod will pick this one up and answer as he has a more scientific brain than me and will give you a logical explination.
Moggie x
Neither.
If we start by accepting that T4 is a storage hormone that has little direct activity, the question really needs looking at another way.
In a mythical "normal" human, around one third of the T4 is converted to T3. So you could argue that T3 is "three times as strong as T4".
When taking tablets, for example, changing from T4 only to mixed T3 and T4, it is common to estimate on the basis of T4 being one quarter the "strength" of T3.
So, 100 mcg T4 (thyroxine) could be similar to 25 mcg of T3 (liothyronine) OR 50 mcg of T4 plus 12.5 mcg of T3.
This seems a reasonable basis for estimating doses but it is no better than an informed guess.
BUT if you are NOT converting properly this falls down. Imagine if you are taking 100 mcg of thyroxine and NONE of it is converting. So you have NO T3. You then take just 10 mcg of T3 and that has an effect which the T4 NEVER had. So there really is no way you can think of one being stronger than the other. One does something; the other does not.
Rod
Glad you said that, Rod. I get very tetchy when people start talking about one being 'stronger' than the other. But so far I haven't been tetchy enough to drag up the energy to say anything. It's like comparing apples and pears. Although I've known people that even attempt to do that! lol
Just to confound things further, I have read that it is about 4 times stronger/more active 
Moggie is right though that Dr Toft advises reducing T4 by 50mcg for every 10mcg of T3 added. Maybe this is just for convenience though as there aren't 40mcg tablets in thu UK? Xx
I think that a whole lot of the T3 dosing in the UK is based on dosage available being 20 mcg rather than anything else. Similarly, in most of the rest of the world, they base it on 25 mcg (with the odd availability of 5 mcg).
Since when did you see a GP who can work out anything other than whole tablets?
If there is too much T4 in the system the T3 turns to RT3 which blocks the metabolism. I am researching this at the moment as have only just convinced GP TO CHECK MY T3 after 30 years of being on Thyroxin. Seems that the proportion of T4 tp T3 can be critical. Any advice on this please
I may have misunderstood - but in my very simple understanding....if T3 is active and ready to use and T4 is stored. or if you have problems converting T4 to T3 - then wouldnt it be easier if everyone was just prescribed T3 and we didnt use T4 at all?
Or have I misunderstood?
I think having some T4 can help smooth things out. Most people can probably convert some T4, albeit more slowly than others, so having some T4 is good as a backup. That's how I see it anyway 
If you take T4 it is possible for your body to control conversion to T3 (or rT3 or other routes) and, therefore, still to help keep you on an even keel.
If you take T3 you have no ability to control the amount of T3 so it is very, very easy to be on a roller-coaster going up and down several times a day.
It is difficult to get an nice, steady state which is working and comfortable to live with.
There are also deep questions over how thyroid hormone gets into the brain with suggestions that T4 is actually better placed to be transported into the brain, and then converted to T3 locally within the brain.
Further, Liothyronine is very much more expensive than thyroxine.
If one thing is clear it is that thyroid is NOT simple.
After two weeks back on T4 only (after a year or so on a T4/T3 combo) my brains ability to convert T4 into T3 seems to be up the swaney, in fact my brain doesn't seem to want to convert anything very well at all, even basic thoughts and actions are getting the better of me at the moment.lol.
Moggie x
Hi Moggie,
Why did you revert back to T4 only, after year on T3/T4?
Thanks for previous reply.
Penny
Heart arrythmia's. It got so bad that my GP has taken me off of T3 to see if it helps BUT, and these are her words not mine "It could just as easily be the T4".
Thyroid meds are well known to interfer with the heart and the reason why GP's dont like giving their patients T3 is because, out of the two, they think this is the worst one.
She originally but me on T3 with a warning of "This can cause heart attacks", a bit drastic I must admit, but those were her words.
If you read questions and blogs on this site often enough the problem will crop up quite a lot, so she has taken me off of T3 to see if this is whats causing the problem. The palps have certainly settled down but they are still there which is making me think that ther is another underlining cause which is Mangensium.
Being low in this can cause heart arrythmia's and taking VitD suppliments can deplete the bodies mangnesium which I was given, by my GP, in HUGE quantities last year, which was around the time the heart palps started.
To complicate matter further I am due an operation in a couple of weeks time for an ovarian cyst which is very large and myself and my GP did not want me going for this whilst my heart was skipping and jumping all over the place and this was the main reason she stopped the T3 - so all in all a right muddle.
The world of thyroid is never easy and GP's in general can make it a lot worse - they either ignore patients symptoms or dont understand it enough. My GP is a good one compared to some on here but she has never once mentioned magnesium - even though it is used in hospitals (before and after operations) to control heart arrythmia's.
Hope I have explained myself clearly.
Moggie x
Hi Moggie,
Thanks, really interesting. My Magnesium usually on low side. Take 450mg/day no Calcium. Shaws reply suggest T4 caused his problems. Can you direct us to where on web can find discussions on T3 affect on heart rhythm.
Regards
Penny
My GP explained it like this: If you use T3 only your bodies ability to convert any T4 its making naturally is made redundant and switches itself off, and that's why GP will be more willing to put you on a T3/T4 combo that T3 only. I suppose it makes sense when you look at it like that (a bit like your wisdom teeth or your appendix) but wether that's just her opinion or scientific fact I dont know.
Moggie x
I don't see how that can be true because that T3 has still got to be converted into T2 and T1 so the body still has to have the wherewithall to convert.
Sorry, don't get the comparison with wisdom teeth and appendix...
Some people no longer get any wisdom teeth as the body no longer needs them and your appendix used to be quite a lot larger than it is now as, like your wisdom teeth, it is redundant so the body has reduced its size. The body is a wonderful thing and if something is not used it will shut it down or reduce it in size until it disappears.
Thats the point I was trying to make - if your system to convert T4 to T3 is made redundant by you taking T3 only then the body will compensate and shut down the conversion process (according to my GP).
Moggie x
THIS is a good point... I've never tried either but was looking into the difference of both, but now I'm more confused LOL. #PSL has them listed for the same price, maybe i'll just stick to hgh.
I found this - yep it isn't simple! .... Regulation of thyroid metabolism can be broken down into the following five steps:
The hypothalamus (a pea-sized gland in the brain) monitors the levels of thyroid hormone in the body and produces thyrotropin releasing hormone (TRH).
TRH acts on the anterior pituitary (directly below the hypothalamus, but outside of the blood-brain barrier) to produce thyrotropin, a.k.a. thyroid stimulating hormone (TSH).
TSH acts on the thyroid gland, which produces thyroxine (T4) and triiodothyronine (T3), the primary circulating thyroid hormones. The thyroid produces T4 in significantly greater quantities (in a ratio of 17:1) than T3, which is approximately 5x more biologically active than T4.
T4 is converted into the more active T3 by the deiodinase system (D1, D2, D3) in multiple tissues and organs, but especially in the liver, gut, skeletal muscle, brain and the thyroid gland itself. D3 converts T3 into an inactive form of thyroid hormone in the liver.
Transport proteins produced by the liver – thyroid binding globulin (TBG), transthretin and albumin – carry T4 and T3 to the tissues, where they are cleaved from their protein-carriers to become free T4 and free T3 and bind to thyroid hormone receptors (THRs) and exert their metabolic effect.
unquote
And the flow from blood through the blood vessel walls into the interstitial fluid.
And the *** active *** transport from the interstitial fluid across the cell walls into the cell interiors.
Thanks for all your replies,
Think supplemental T4 a problem if you have T3 uptake problem.
The T4 just gets in the way!
Just reading through some of the stuff on here just totally blows my mind and does my head in equally....
I hate this chuffing illness and will never ever understand it, and feel I am a fighting a never ending battle! Grrrrrrrrrrrrrrrrrrrrrrrrrrrrr
T4/T3 Combo Synthetic Vs NDT choice
Cardiac side effects T4 vs T3
Adding T3 to T4 for the first time
T3/T4 blood test timing 
T4/T3 morning dose time 
