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Thyroid UK
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I've been very reluctant to write this post because the issue seems so obvious to me that I must be wrong and will look like a numpty.

Please bear with me while I ramble through my very questionable logic :)

NDT is extracted from the thyroid tissue of a pig, dessicated and formulated into standardised tablets of 60 or 65 mcg - 1 grain.

In general terms, each grain (tablet) contains both T3 and T4, together with other hormonal elements. The ratio of T3 to T4 is approximately 1:4 (eg 9 mcg T3 : 38 mcg T4). My understanding is that nothing is 'added' - ie the T3 component is an integral part of the extract.

I similarly understand that the some T3 is produced in the human thyroid gland - approximately 15% (ie ratio of about 1:7) - clearly significantly less than that produced in porcine thyroid.

In both cases, the remaining T3 requirement is met by conversion of T4 to T3.

I can see that, for purposes of people who are calculating their dosages for transition purposes, the references to the specific T3 and T4 content are needed. However, thereafter, it's surely just an added confusion.

No-one would take Levo in divided doses, so why is it thought necessary to split doses of NDT to distribute T3 throughout the day?

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As I see it the t3 part has a much shorter half life than t4 and it gets into the blood stream much quicker too. By taking just one dose a day you risk getting large peaks and troughs, ie, over and under medicated. The t4 has to be converted within the body into t3 and arrives into the blood in a much more controlled manner.


But isn’t that the same with Thyroxine?


T4 is thyroxin. Levothroxin is the synthetic form shown as Lt4 sometimes. T3 is liothyronine.

T4 is known as a storage hormone or prohormone, it is biologically inactive for the most part. It is converted by your body, mostly your liver into t3.

T3 is what every cell in your body needs.

It takes your body something like 7 days to convert t4 into t3, and is considered to have quite a long half life.

T3 has a half life of about 12 hours, so if you take an amount say 20 mcg it gets int your blood stream in maybe less than 2 hours, 12 hours later you only have 10 mcg in your blood stream and 12 hours after that you have 5 mcg in your blood stream. On top of this your body is actually using up the t3 to perform all the tasks required to keep you alive and healthy.

So the real picture is that by taking your NDT in one dose, just looking at the t3 part of the dose you go from an overdose to virtually nothing over 24 hours. Hyper symptoms to hypo symptoms every 24 hours, not good.

The t4 element of the dose you are taking dose help out in smoothing out the dosing but you do still have this effect of being over optimum then under optimum ever day.


I can vouch for this. If I don’t split my dose I’m in trouble.

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I think that this link may explain my thoughts more adequately than me.

I didn’t get my ideas from there but they do seem to summarise an alternative view.

Thank you for your patience 😊

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I've heard the half-life of T3 quoted as 6 hours. So it could be even faster than you suggest.


The cellular content must be considered. The figures quoted in this thread refer only to T3 levels in blood stream.


Yes, all the figures quoted are for the blood stream. Very little is known about what happens inside cells, because it can't be measured.

But for the question you're asking, why do people multi dose NDT and not Levo, you don't really need to understand.


Very good post indeed! I have been wondering the same things myself.

As others have pointed out, the advice to multi dose NDT is due to the fact that T3 is said to have a very short half-life (anything from 12 to 24 hours depending on source), whereas T4, which is basically inactive until it's converted to T3, has a half-life of several days, even weeks.

Some feel better when multi dosing NDT, while others don't notice a difference and feel fine taking it once a day. I have always taken thyroid hormone replacement one a day, in the morning, and I feel fine that way, even on NDT. So I guess it's highly individual.

Porcine NDT contains a higher T3 to T4 ratio than human thyroid, but I have come to believe that poor converters (many hypothyroid patients don't convert T4 to T3 very well, which may be the reason many patients on T4 only feel miserable although doctors declare their lab results are optimal) may need the higher T3 ratio in pig thyroid....that definitely seems to apply to me.


I’m a poor converter on T4 only. On 120 mcg Levo, had an FT3 of 4 and an FT4 of 30. Quelle horreur.


Oh dear. Sorry to be so dense but I just do not understand. Guess I’m saying that NDT works in the same way as human thyroxine - not Levo.

I’ve been on combo doses of synthetic T3 and Levo and had to multi dose or crashed badly. However I’ve never had to multi dose with Levo and don’t know anyone else who has.

Forgive me Greybeard. I must be having a brain fog day. Thank you for trying to explain.

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You could think of ndt as midway between the two. You need to take a bit more care than t4 but less care than t3. As others have said some people can get away with dosing once a day others can't. Just be honest with yourself and be careful.


Good morning Greybeard and all

Just thought I'd let you all know that I've had a great night's sleep and took my 2 grains in one dose at 6.30 am two hours before breakfast.

Previously I was having one grain at 7 am and the second at bedtime (10 pm) and then lying awake most of the night.

Can't say I was particularly 'running low' during the day on 1 grain in the morning (have been falling asleep during the odd film but that's normal for me,)

Hoping that the once a day dosing may increase my energy during the day and leave me ready for sleep at end of day.

Many thanks for all your thoughts.

Will keep you posted x


I found I could take up to 2 grains in one go no problem, but over that (even just a quarter) and I get a headache 4-5 hours later, took me ages to twig to that one because of the time delay! I dont find the split causes sleeplessness, just goes to show we are all different.

If you find you don't tolerate a single dose there is nothing to say you have to split evenly or so far apart.


T3 has a half life of approx 6 hours.

T4 (Levo) has a half life of approx 6 days.

What this means is that T3 gets used up in your body much more quickly. T4 hangs around for a long time, so it doesn't matter if you skip doses, or take a double dose by mistake, it all evens out.

T3 goes to work very quickly, and you may feel the difference almost immediately. But it also passes out of your body very quickly. Some people can feel themselves getting more and more tired 4 or 5 hours after a dose. Others don't.

NDT contains both forms, plus other things. Some people need to split their doses with it, and others don't.


But while T4 is 'hanging about', it is converting to T3 and, in the case of NDT, compensating for the fast processing of T3.


If all is going well, the T4 conversion to T3 is a bit like having a load of tinned food in your cupboard. You only take something out and open it when you need something. It doesn't get instantly converted to T3, it's a slow and as-needed process.

Following the analogy, T3 is more like a cream cake. You have to use it up quickly after you've bought it.

I don't understand what 'compensating for the fast processing of T3' means.

In practice, although these are theoretically quite interchangeable chemicals, people's bodies will not handle them completely perfectly.

For someone who needs to take T3-only to feel well, no amount of T4(Levo) will be a good substitute for it. So for most people who take NDT, they are probably benefiting more from the T3, and running mostly on T3-only. Not much of the T4 turns up in the blood stream, so it's probably not even being absorbed.

If you find it hard to understand, I suggest just continuing to read the forum. These things slowly sink in once you've read them many many times.


A good analogy. I was doing well on T3 only multi dosing. I couldn’t tolerate T4. I’ve had to go to NDT because I can’t get T3. It’s very expensive to buy. I buy NDT but price is more realistic.

There is about 18 mcg in 2 grains of NDT which means that when I was dosing twice a day I was taking 9 mcg (plus of course the T4). There is no way that I could cope on that T3 dose, even twice a day, so the T4 element must be making a significant contribution

It’s a complex subject and it becomes more so because everyone has different experiences which inform their thinking


Hello again

I’ve just read your history and thought it was mine 😂. Probably only difference being that my thyroid cancer was diagnosed while I was being treated for breast cancer.

I too went down hill rapidly with only one lobe and it was a relief when the histology result came through and they dug out the other lobe and gave me replacement meds.

I too suffered the mess ups of varying doses and meds. I got very tired and depressed and they treated me with Prozac. I got more and more tired and my body was wracked with pain. Life stopped. Every time things got worse they increased the dose - and I got to the point where I thought I would never walk, think or indeed live again

The endos and oncologists carried on tinkering with my thyroid meds and when there was no improvement basically gave up trying and decided I had fibromyalgia and chronic fatigue

This went on for three years. 6 months ago I decided to wean myself off Prozac. Boy. Was that hard. Although I did it slowly, I suffered discontinuation syndrome and pain and anxiety leapt to new heights.

Eventually I was Prozac free and the difference was amazing. Still tired and achey but alive again.

Then the T3 debacle started and I changed to NDT. This has been the icing on the cake.

Not only do they dose us inappropriately on synthetics, they destroy our bodies with other drugs which we don’t need.

The potential of Prozac to cause symptoms of fibromyalgia and cfs are not well known - but when you research widely the evidence is there.


That's interesting, Grincho. I couldn't believe it when my consultant told me there was no more she could do to treat my illness - which she had actually created, as a way to treat an illness that didn't really give me any trouble :p

I've just come out of seeing a theatre piece about cancer. I found it very disappointing, because most cancers are so different from thyroid cancer - once a person recovers from it, they can live a normal life. And many people are walking around, doing normal things, even during the treatment. I find some of that very hard!


I agree. They call it ‘the good cancer’. The survival rate may be good but life after TC is never as it was before.

I have no ‘fall out’ from my breast cancer. It’s forgotten, , done, finished. I never think about it now.

I feel defiled, stripped of my physical and cognitive ability.

Life is precious. Quality of life is the pinnacle we hope for. After TC it’s gone


Yes, the quality of life measures are one of the lowest for any cancer. Doctors have that innocent, puzzled attitude to why that would be, but it's very obvious to patients that its because the hormone replacement treatment doesn't work :p Or just as often people are left on inadequate doses.




I've never taken T4, though my experience is that 1 grain of the NDTs I've tried

feels slightly more effectiver than 25mcg of T3, especially with regard to body

heat & skin issues.

I take both NDT &/or T3 first thing,. Some people split doses or take it at bedtime to see if that way suits them better, Neither way is compulsory, it's just a matter of preference.


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