Thyroid UK
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How long does reverse T3 last and why isn't it T3 that needs cutting not T4?

Hi, I am confused by the reverse T3 debate. I realise that the reality is that so far we don't actually know as much about it as would be useful, but I have two questions.

1. Does anyone know how long Rt3 lasts in the body, does it die of its own accord the way T4 and T3 will or does it simply block receptors indefinitely?

2. Unless your problem is a conversion issue why does going T3 only resolve the problem shouldn't it be the other way round? What I understand is the RT3 is a mechanism to prevent too high a take up of T3, a safety mechanism by the pituitary gland to ensure hyper symptoms are limited as much as possible. Therefore the pituitary senses too much T3 and converts T4s into RT3 for the very purpose of lowering take up. This can obviously go wrong. I suspect that I have been on too much T3 to T4 ratio for 13 years, resulting in too much RT3 being made and blocking my body's normal function.

If that hypothesis were the case (and it's not because for some reason I am converting T4 to RT3 for no good reason) - why would taking no T4, and going only T3 be the solution? I have read posts by people saying they do this - ( and I'm leaving to one side the people who thrive on solely T3 indefinitely, perhaps because they simply can't convert or aren't producing T3) - and feel great for 4-8 weeks but then have to go back to combo as things don't feel right. They interpret this as having cleared out the RT3, leaving their body needing both T4 and T3. This doesn't make sense to me, surely if RT3 is made by sensing too much T3 the solution is to cut T3 for a time to allow the body to stop making RT3 and get itself back in balance before adding increasing amounts of T3 back to find the right spot?

Since unless your thyroid has been removed or completely stopped functioning your body will still be making some T4, if you swamp the body with T3 you are potentially going to get it making the T4 it does make into RT3 as a reaction? So slowly - because obviously as a hypo person you don't make loads - the body will build up RT3 from the T4 it is making. Initially this may lead to a drop in T4 because there isn't so much of it to convert, but it will not stop the body from thinking like a toxic body that wants to make as much RT3 as possible in order to block take up of T3.

On the other hand if you cut all T3 for a while the pituitary has no reason to convert the T4 you are taking into RT3, it can gradually lower the levels of RT3 that have built up as it senses there is a need for T3 conversion to take place. Then when it has got itself back in balance you will need to start adding very very small amounts of T3 to find your body's balance that is getting enough T3 into your cells, but isn't swamping the body with T3 triggering a RT3 reaction.

As with all these things I suspect we are all different and our bodies will each need its own unique combo balance. However, I can not see the logic of swamping the body with T3 as a way of preventing RT3, you are still putting your body in an unnaturally hyper alert state. I suspect my body has been given too much T3 and that this has caused my rise a rise in RT3 leading to me being very ill over time, triggered by massive stress events to the body.

If anybody knows what we actually do have evidence for about RT3 I would be really interested to hear it, as I am really trying to get to grips with what has happened to me and the best way to solve it.

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The raw material required for the body to make both T3 and Reverse T3 is T4.

T4 is referred to by this name because it is made of a Tyrosine molecule with the addition of 4 iodine atoms.

To make T3 the body knocks one of the iodine atoms off of T4.

To make Reverse T3 the body knocks a different iodine atom off the T4.

So, the logic behind taking T3 only is that the body will not have the raw material necessary to make Reverse T3.

Hope this helps. :)


Yes, I know that about the iodine's etc, but that doesn't answer the point that the body is highly likely to be making some T4 of its own, which it will then be desperately wanting to convert into RT3. You can only assume that it works if you can prove your body makes no T4 of its own at all. If it is too much T3 that triggers the need to make T4 into RT3, it is the removal of alien T3 that will trigger a halt in RT3 production


Taking t3 often artificially suppresses TSH which means that the thyroid is not likely to be making enough t4 to do this.

Using t3 is not something that works for everyone and I suspect of you are producing significant amount of t4, it would not work well for you.

Everyone is individual.


Yes that's an interesting point about TSH being surpressed :-)


To add to what humanbean says, it can take up to 3 months to clear reverse t3 apparently. It does sit in the receptors for a while but doesn't block them as such. It just competes with the t3 for a space on a receptor. Once your reverse t3 is at a desirable level and your T3 is good, you should start to feel well again, all things being well.

Reverse t3 is important for regulating metabolism so, in a perfect world, we would all need some t4 to make that reverse t3. Unfortunately it is not a perfect world and some of us just cannot tolerate t4 at all. This can make dosing a little tricky for some.

I hope that helps

Carolyn x

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Too much t3 will only cause too much reverse t3 if there here is also t4 present. For people with reverse t3 issues, t3 only treatment is often the only thing that works.

Things that can cause high reverse t3 include selenium or zinc deficiency, cortisol issues, stress, dieting, low iron, chronic illness and probably several more things.

Swamping the body with t3 to cause a hyper state is NOT a good idea. T3 treatment is a viable option (the only option for many) but patients should only be given the dose that makes them well without giving hyper symptoms.

Swamping the body with t3 doesn't clear reverse t3 any faster. In fact it is advisable not to go too high a dose until reverse t3 has cleared to avoid becoming suddenly hyper when the reverse t3 finally clears.

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I suspect that looking for hyper symptoms is a red herring - that's why I thought I wasn't on too much T3 to T4 ratio, because I expected the problem to be going hyper and I was on the look out for those kinds of problems. However I wasn't expecting the symptoms to be hypo ones and then some, so I had no idea that I was on a bad dose because I have been hypo for 20 years I thought I knew what being hypo was like and that there must be something else causing me to be so ill. But now I suspect my dose is at the root of the problem and why I have lost the last 3 years of my daughter's life. I may be wrong, I will find out after a few months if I stay very ill.


If t3 is making you I'll you should probably stop or reduce the dose or talk to a doctor with experience in this area. T3 isn't for everyone. It can make some people very ill.

Do you have blood test results including iron ferritin, folate b12 and vitamin D? If these are not right reverse t3 is more likely to be a problem.

Have you done a saliva cortisol test to see what your adrenal profile is like? If your adrenals are not great, you will struggle with t3 unless you take things very slowly and support your adrenals at the same time.

Do you know your T3:reverse t3 ratio? Unfortunately reverse t3 testing is only available privately in the UK.

A lot of the hyper symptoms are similar to hypo symptoms. Any deterioration should be taken as a sign that the dose isn't right for you and needs changing. Many hyperthyroid patients will tell you that they experience many of the same symptoms as us including fatigue and aches and pains.


I can see that being the case if your body has a problem with T4 or struggles to convert - but many people post about feeling lousy again once they get to a certain point of being T3 only, that would seem to suggest their body is now tipped over into making RT3 again. I'm not convinced that this makes it logical to up T3 unless you can't tolerate T4. But to be honest unless we all titrate our doses from scratch in a very small and controlled way - and upping by 25 mcgs at a time is not small when you consider how sensitive the body must be in it's own functioning - what evidence do we have as individuals that we just haven't got our combination right? At the end of the day we are in the dark attempting to find something that makes us feel good, my point is that if you T3 only for several months and then start to feel iller perhaps that's not the most logical or sensitive way to respond to the body.

I'd be really interested to know how long RT3 lasts compared with T3 and T4 and where that evidence comes from. I think all this is fascinating and seems very little is truly known about it. Anyone point me in the direction of some research papers?


2043 papers on RT3:

The actual link would break if posted so I have done so as a preview tiny URL - that lets you see where it is taking you before you go there. As the link is to a search, there may well be irrelevant papers but it is a start.

What we have relatively poor evidence for is how the body controls the balance of T4/T3/rT3 and so on.

I suspect that we actually have a problem in understanding exactly how conversion is controlled, why the brain seems to do quite a bit of its own conversion, etc. We really only have a few bits of the control mechanisms relatively well sorted out - and even then, clinical practice seems to ignore them all too often.

I rarely enter rT3 discussions for one simple reason: I don't believe that I understand sufficiently to be of any use. Much of the time all I could say would be "I don't think it is as you have said" but without backup and certainly without being able to offer alternative views.



Thanks Helvella, yes I think it's important to acknowledge that basically we are all bumping about in the dark and can't make concrete statements. But I also think it's good to reason and think and try out hypothesis - it's just such a shame most of the medical profession aren't questioning and thinking in this way, let alone research bodies. Oh of course forgot, no profit in that so Pharmas won't fund! :-)


There's also the issue that if research gets done it is peer reviewed before standing a chance of being published. The peer reviewers are often the same people who we are fighting against. If they don't agree with the research they don't have to publish.

I know they are supposed to be unbiased but the sad truth is that they aren't all. When I was a research physicist, I was warned to never put my first name as they didn't take women seriously as physicists (or scientists in general). That was 20 years ago but it is still a problem :(


I completely agree. 25mcg dose increases are too big unless you know you have thyroid hormone resistance. T3 should be increased slowly!

I also agree that if t3 makes you worse you should stop. It doesn't suit everyone. I firmly believe that everyone is an individual and that there are too many things that could possibly affect the conversion to reverse t3 to know what would happen to a particular individual in any particular circumstance.

For me, t3 had been a life save but I am one of the minority that cannot tolerate t4 at all. I suspect this may have something to do with my TSH always being low, even when clinically hypo but I don't know for sure. I only know that I feel best on t3 only, just like many people feel best on t4 only or combination therapies.

If I was feeling so I'll on t3 I personally wouldn't wait a few more months to see what happen. I would stop. If you feel worse than it's doing something your body doesn't like.

What is your current regimen?

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This is also an explanation by Dr Lowe re reverse T3.

If you go to the date March 24, 1999 on this link for the explanation:-


Thanks Shaws, that is very interesting about the tests he has had done for Rt3 - I had severe Bulimia for many years as a teenager, I'm sure that didn't do me any good, then three major abdominal operations in my thirties one of which I was dangerously ill with septacemia and was on IV antibiotics for two weeks solid in addition to all the oral ones I'd already been given. I am sure the operations have something significant to do with triggering my M.E. I have always thought this, perhaps on top of being Hypothyroid for 17 years prior to that? I have never been sure what the difference is between M.E/chronic fatigue syndrome and fibromyalgia. What does Dr Lowe recommend as the treatment for FM out of interest? Perhaps it would be relevant to my M.E/CFS?

All information is grist for the mill.


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