Thyroid UK
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Reverse T3 question

With the understanding that I've not been tested for a few months but that my last fT3 result was 4.7 (3.5-5.5)...

I feel dreadful: the kind of tiredness that I usually feel after extreme insomnia, fuzzy, unable to construct a coherent sentence at times. Also pulse dipping to low 60s and temperature now normally below 36.5c, which is low for nowadays and getting cold chills. Very slowly putting on weight and unable to shift it.

I know very little about reverse T3 but wondered whether it could be the reason why I feel so rubbish. I'm planning on getting it tested when I next get my fT3 tested. With the amount of both T3 and T4 I'm taking (10 mcg and 150 mcg respectively) being seriously undermedicated seems unlikely. But it's starting to feel like it did when I was first diagnosed 😔

Ferritin, vitamins should all be at good levels as supplement daily with decent dose.

Any ideas? Given the temperature and pulse thing I'm inclined to think that it is thyroid-related.

20 Replies

Hose, you can be undermedicated on your current dose and, if the Levothyroxine isn't converting, the unconverted T4 could be causing high rT3.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

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I'm sorry you're feeling so bad. You would have thought having T3 added would have helped but it may be due to the fact that the ratio of T4/T3 isn't sufficient for you. It may be that you might feel better with more T3 less T4, i.e. if you go to page 80 on this link and on the top of the left-hand column read the result of research:-

In fact this whole paper is full of good facts which I, as a sufferer, can wholly associate with. An excerpt at the end of page 82 - following on to page 83:-

T3 Treatment’s Alleged Heart Attack Danger

Excessive T3 has also been associated with heart attacks. A long-term study of 1,569 patients treated properly with establishment-dismissed desiccated thyroid showed a significantly lower rate of heart attacks than found in the five thousand subject Framingham study. Based upon the

Framingham study, there should have been 22 heart attacks among the 1,569 patients instead of only four. Furthermore, patients who quit taking desiccated thyroid had heart attacks more often, nominally at the Framingham rate.

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Thanks, Shaws. Given that you cannot tell me what to do, but on the basis that you have personal or anecdotal experience, how might I best go about rebalancing my medication levels?


I suppose the main question would be whether it's better to keep T4 at the same dose and increase the T3 a bit or drop the T4 a bit and increase the T3 rather more?



Sorry to hear that you feel so unwell.

You mention Iron & nutrients but what about adrenal issues.? If your meds haven't been working properly you may have compromised cortisol levels. When you don’t make enough cortisol, thyroid hormones can pool high in your blood and your body responds by converting the T4 to excess RT3.

Low cortisol levels and high RT3 can cause chronic anxiety, poor coping skills.

What about insulin & blood sugar levels and any gut issues? IBS or candida ?

Do you have low stomach acid or malabsorption issues?

What about female sex hormones? Is your monthly cycle regular or are you menopausal?

Do you have a high thyroid antibody count ?

Any of these can impair the synthesis of thyroid meds.

Approximately 85% of circulating T3 is produced by monodeiodnation of T4 and the small amounts converted and unused are usually eliminated quickly by the body. You are taking a lot of T4 to feel so unwell so must assume some is possibly resulting in high RT3 which could bind to the T3 receptors blocking the action of further T3.

When too much RT3 is produced, it becomes a vicious circle as the RT3 competes with T3 as a substrate for the 5-deiodinase enzyme and will inhibit the conversion of T4 - T3.

Taking less T4 and more T3 will help eliminate RT3 from the body and encourage T4 to convert.

However T4 is not always to blame for high reverse T3.  High levels of T4 can lower D2 enzyme activity, which lowers T4 conversion to T3.  But high levels of T3 will raise D3 enzyme activity, so more T4 is converted to reverse T3 to keep T3 levels normal.  In other words, neither T4 nor T3 can be too high, or the appropriate enzymes are invoked to keep the levels where the body deems appropriate.

Eat protein at every meal as it helps to boost T3 and also convert T4.

Supplementing selenium is known to help with T4-T3 conversion.

It is important to take your meds on an empty stomach with a glass of water, 1 hour before food, 2 hours before supplements and 4 hours before calcium, iron or vit D supplements.

If this were me I would reduce T4 & increase T3.


This following link explains the importance of vitamins and where they may be obtained. This forum is supported by the charity ThyroidUK. You do not have to join the charity to benefit from this forum but by doing so you will be supporting the charity and also entitled to various discounts when buying supplements, as detailed in the link below.

High T4 & RT3.


Adrenal: did a 24-hour salivary cortisol in the summer, three out of four readings over range and DHEA to cortisol ratio low.

Periods (withdrawal bleeds, technically) hugely erratic on pill that I'd been on for years, will be tested for early menopause shortly.

Insulin and blood sugar control: I am already pre-diabetic but without most of the associated conditions that go with, such as excess weight, lack of exercise, too much visceral fat, high blood pressure, etc. Have had to drastically lower carbohydrate intake to get bloods down again so eating lots of protein with every meal.

Still have high level of antibodies (540-odd at last count in the summer), which is well down on diagnosis 20 years ago when TPO-ab level was over 400,000.


Gosh hose,

I have never heard of antibodies that high. You must have felt dreadful.

You have lots of reasons why thyroid meds may not be working quite as they should.

I eat protein at every meal too ( & still have a high TPOAb count ! ).



I will state I have absolutely no medical training and can only give my own experience.

I felt dreadful on levo alone and couldn't believe how much worse and far more symptoms I had than before I was finally diagnosed with a TSH of 100. The addition of 10mcg of T3 to 50mcg of T4 (I was originally on 75mcg of T4 and it was hell) and I immediately felt so much better. After my next blood test I was phoned to stop T3 immediately, I refused so was told to reduce Eltroxin (T4) to 25mcg (which combined dose would have been about 55mcg levo). I had only found out about T3 through as the forum hadn't started then. My search for further info began. The more I reduced levo and increased T3 the better I became. I didn't need too much T3. I also did things slowly.

I saw two private doctors (one who didn't prescribe) and another who took into consideration clinical symptoms particularly if the patients were denied thyroid hormones due to the TSH only. Unfortunately he has now died. I tried several NDTs - and I know one which suits.

I now take 37.5 T3 (1 plus 1/2 tablet) once daily. 25mcg T3 is around approx 75-100 in its 'effect'.

Whatever you decide it should be gradual. Either reducing T4 gradually whilst replacing with an amount of T3. Many do fine on T4/T3 combination. You should always take your temp/pulse several times a day when introducing T3 as sometimes you might feel quite hot but temp hasn't raised. If you get palps that would mean a reduction. Always be aware of how you feel and once you reach a dose you should feel normal health with no symptoms. If you've taken a little too much just miss the following day's dose or reduce it.

I found T3 extremely calming as I had constant palps when on levo.

I hope you find your optimum level of whatever you decide.


Dear Shaws, I am taking T4/T3, but in a proportion that seems to be wrong. I am considering raising T3 and lowering T4, or even taking T3 alone, but fearing that might be a problem: doesn't T4 have functions of its own, apart from converting to T3? I know many people take T3 alone, but couldnt it cause other problems? thank you!

(I have described my situation on other posts, but basically I have secondary hypothyroidism (TSH doesn't work at all) and a conversion problem (T3 always too low.))


miriammsm, I'm sorry you've not yet got to an optimum of thyroid hormones. T4 has to convert to T3 and sometimes it doesn't sufficiently for us to feel well.

Dr Lowe discovered as a very young man that he himself had thyroid hormone resistance and took 150mcg of T3 daily. He was also an Adviser to Thyroiduk but died due to an accident.

Excerpt from

The second possible reason for your bad reaction to Synthroid is that T4-replacement simply won’t work for you. It doesn’t work for many hypothyroid patients. In a recent study in the United Kingdom, for example, T4-replacement left 50% of patient suffering from hypothyroid symptoms (Saravanan, P., Chau, W.F., Roberts, N., et al.: Psychological well-being in patients on ‘adequate doses of L-thyroxine: results of a large, controlled community-based questionnaire study. Clin. Endocrinol. (Oxf.), 57(5):577-585, 2002.) Unfortunately, through faulty reasoning, these researchers concluded that a much smaller percentage of patients suffered from symptoms despite being on T4-replacement. They are mistaken about the percentage. The evidence is overwhelming that T4-replacement is the lousiest approach to thyroid hormone therapy. I’ve documented the widespread failures of the approach in two critiques:

Moreover, you’ll most likely react badly again.

and T4-Replacement forsakes many patients.

But most patients recover quickly with T4/T3 products such as Armour Thyroid, Westhroid, and Naturthroid, and with T3 alone—as long as the patients use high enough doses of the products. If your doctor will cooperate and treat you with one of these products and ignore your TSH level, you’re not likely to have another bad reaction to thyroid hormone therapy. Instead, other factors held constant, you can, I believe, expect a highly positive treatment outcome.

Read the first two answers on the link below:-

This is T3 only.

You will see that T3 isn't dangerous. I feel very well compared to levo - night turned into day. Of course, some do better on NDT but we have to try an alternative if levo isn't working.



Thank you a lot. I'll keep trying. I definitely need more T3.


20mcg tablet of T3 equals approx 60mcg of levo

25mcg " " " " 75-100mcg levo.

Therefore if you add, say, 1/2 tablet 20mcg T3 (approx 30). The reduction of T4 would be 25mcg of levo (as levo normally comes in 25mcg, 50mcg and 100mcg).

I would keep to any change for 2 weeks each time as it's best to go slowly rather than get overdosed. Once you feel well remain on that dose. If you get palps/feel too hot (take temp/pulse to make sure it's risen) reduce back one dose.

"I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions"

(see response to Hose below too)


Thank you! :)


Is there any value in taking my T3 dose in the morning instead of at bedtime? Might it give me just a little more pep? I'd prefer to not change my dose before my next blood test (a couple of weeks).


I don't think it makes much difference whether morning/night. It's the person's preference, i.e. it's more convenient for them.

The action of T3 once it's in our receptor cells, lasts for between 1 and 3 days.


I was originally taking it in the morning but then I started a new antidepressant (bupropion), which overstimulated me when taken at the same time as the T3. I think that effect will have settled down now.


Forgive my ignorance, but do I really need to reduce my T4? Can't I just increase my T3? What are the pitfalls on this approach?


Hi, hose1975

It is a big learning curve for us who have no medical training - stumbling along trying to improve. This is what I think or understand:-

If someone is taking, say, 150mcg of T4. Feeling unwell, still has symptoms etc. They may be completely unaware that they might be very near a maximum dose for them and add 10mcg of T3 (taking their dose to the equivalent of approx 180 levo which might be too much for them and they'd get very unpleasant symptoms and believe T3 was of no benefit and stop.

Therefore, if they reduce 150mcg of T4 to 125 plus add 10mcg T3 (half a 20mcg tablet T3) - dose is 155mcg combined. They stay at this dose for 2 weeks and if they feel no benefit can add 1/4 T3 for 2 weeks and always, taking note of temp/pulse (which you should begin to do several times a day before adding T3). If there's any stimulation, i.e. too fast pulse/heart/too hot they can either reduce their T4 slightly or T3. The best way to know if you're on the right dose, is relief of symptoms and a feeling of well-being. Our minerals/vitamins also must be at optimum too as we can be deficient which also causes problems.

(see my response to miriammsm above)

"I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions"


How should we judge, then, when to stop dropping the T4 down? Thanks for the above, it is useful, but I am so confused! Would it matter particularly if I stayed on my pre-T3 150 mcg T4 dose and just upped the T3 by 5 / 6.25 mcg (depending on brand of tablet) every few weeks?


You could try and see - I don't think there's much harm in that.

re 'stop dropping' down the T4. You stop when you're feeling well with no symptoms. Usually you don't need to drop very much because the action of the T3 is direct (it doesn't have to be converted)


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