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Unpleasant 'reaction' to T3?


As a result of secondary hypothyroidism I have been taking T4 (150) for 2 years. Upon advice from the forum i dropped this to 125 last week in preparation for starting T3. My Endo thinks i might not be converting so recommended a 2 week trial of T3 5mcg twice a day but i decided to halve that to 2.5mcg twice a day (morning and lunchtime).

Today was the first day and i just want to check that what i think is a reaction to the T3 is 'normal' even on such a small dose.

In summary i have felt very weird: increased heartbeat, spacey/dizzy, sweating, nervous/anxious.

Is this ok? Will the symptoms die down over time or does it sound like T3 is not for me??



27 Replies

How soon after taking your dose of T3 did the reactions occur?

The reactions may be as a result of your body using up the T3 and wanting more. Also, you've reduced your Levo by 25mcg per day and replaced it with the equivalent of about 15mcg per day (as a result of the 5mcg T3 you are taking), so have reduced your dose over all.

I get the impression that you were nervous and anxious before taking the T3 anyway, because you decided to reduce your dose by half. T3 isn't that dangerous, particularly at the miniscule doses you are taking.

And of course, people do get symptoms from taking new thyroid hormones for the first time. But they do adjust and adapt. You can't really decide on the basis of one day that T3 isn't for you.


Thanks. I took the first 2.5 at around 9am and didnt notice much and then the second 2.5 at 1.30pm and thats when the reactions occurred.

I see what you are saying about the change in overall meds but there are so many different suggestions i find it difficult to navigate what might be best for me.

My main curiosity was whether others had a 'reaction' when first taking T3.

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Yes, it is well documented, but I don't think I can find the documents at the mo! T3 speeds things up and can result in a higher heart rate - don't panic!

Dr Lowe had good info on this - I hope @Shaws chips in.

I even took T3 with milk to start with, just in case of an adverse 'reaction'. I think you've jumped in at the deep end a bit, reducing your T4 by 25mcg can cause stuff too (adrenals compensate) and 25mcg/one T3 tab can be 4-5 times as potent as T4. I prefer NDT which has both in natural form (for me anyway).

Good luck with you titrating, takes awhile to hit the sweet spot, you'll get there I'm sure with all the helpful advice here.

J :D


I think you would have been better staying on the 150 T4 and using a very small dose of T3 to start with. I would be looking to use just 2.5mcg T3 per day along with your T4 dose.

You have made 2 changes to your meds and it is always better to make one change at a time.

I use a very small amount of T3 (3mcg approx) and i seem to go against what is generally the norm, but i have read Dr Blanchard's book called functional thyroid and he believes in very small doses of T3 along with the T4. He says ideally patients would start on 0.1mcg of T3, but they don't make such small amounts.

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Thanks for the reply.

My Endo wanted me on 150 T4 and 10 T3 but following suggestion in the forum i decided to try 125 and 5. Im finding it quite difficult to make sense of all the conflicting strategies.


I have read your others posts and it seems you do have a high over range level of T4. 125 T4 may well be a better amount for you. A rough dose of T4 is 1.8ncg per kg body weight.

The other issue you have is that you do have some blood tests which show your Ft3 is in the 5 area and this is where it wants to be ideally. You also have some low FT3 results.

I would prefer to go on how i feel and if the T3 is making you jumpy, the best course of action is to lower or back off for a day or two.

As i said before many people don't need as much T3 as is often put forward on the forums and this is often the reason people are not getting better. The best way of working out what you need is to always start low. 5mcg is seen as a low dose, but really you want to be looking at using half that. A 98:2 ratio of T4 to T3 is something Dr Blanchard was recommending.

Men often don't need as much T3 as women as we convert well. This is the case for me certainly.

I understand there is a lot of conflicting info out there. I will say we are all different. There is not one protocol which suits all people. Knowledge of the protocols is the answer you need. These are the protocols i know of:

T4 only

T3 only

T4/T3 with a similar mix to that in NTH (4:1) but you can work out a specific ratio to suit.


T4/T3 this uses a very low dose of T3 mixed with the T4. The ratio is approx 98:2.

I would also recommend taking your thyroid meds at bedtime. Certainly worth trying, but don't do it until you find a T3 dose which you are happy with. Then maybe give it a go. always make one change at a time with your overall routine.


Trademole, You do sound a bit anxious and I can understand that. There is so much hoo-ha spoken about T3, and with it not being available at present “legally” via prescription in the UK... well it does make it sound dangerous. But it’s not; not in prescribed doses, and a total of 10mcg a day, split into two doses is well within conservative range. My endo started me off on 20mcg a day in 4 split doses.

I was extremely nervous myself initially. I’m in Australia where T3 is freely available but I still felt anxious taking something that has such an immediate effect (within hours) vs T4 which takes weeks.

Two or so months down the track I’m on 2 grains NDT and 60mcg T3 which I take at 4am all in one go and then go soundly back to sleep. THAT’S how resistant my tissues are in taking up T3. ***I have ZERO medical qualifications and note that we are all different and different things work, or don’t (Eg my dosing vs marsaday ’s ... go figure).*** I just wanted you to know that my head has not blown off and both my endo and I am pleased with my progress :-)

My experience with T3:

* Anxiety lessened over time as I adapted to the increasing dose, and I realised that T3 is not speed. It is a legal, useful hormone that my thyroid can no longer make any or enough of for my body.

* Yes, my heart-rate increased and might be still increasing, but coming off a low base of around 60 (no, I am not a marathon runner :-/ LOL ...well my Lordy you would WANT your heart-rate to increase wouldn’t you?!!

* To manage my initial anxiety, I agreed a few simple indicators of HYPERthyroidism or too much T3, to look out for with my GP (I do the “small stuff” with my GP and leave the big picture to my Endo AND have them write to each other. That way I feel confident my whole health picture is being cared for; it’s working well now. ):

** extreme diarrhoea for 3 days

** blood pressure going way high; he checks me regularly, and you can do that at the chemist too

** “buggy eyes” eyes starting to bulge, as they can do with hyper/Graves.

Although I continue to feel my body changing — like I’m coming out of deeeep hybernation — and it does feel weird, uncomfortable sometimes; I just review my checklist (okay, all good, on we go) and look to my diet, 8+ hours sleep and meditation to manage any anxiety. I’m progressing slowly but surely.

I hope this helps and I hope you feel better soon. Take care of yourself Trademole.



Blue_Bee, I believe the bulging eyes of thyroid eye disease are caused by the antibodies of Grave's, not by the high level of hormone.

I may be wrong as I've just been doing a quick search because I've wondered about this specific symptom could be caused by over medication.


This was on what seems like a good website

The amount of TSI present in a TED patient correlates with TED severity.

However, sometimes TED can occur without TSI formation.

So none the wiser!

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Thanks for looking it up Silver_fairy! I'd like to know as I am pushing my freeT3 over range. I'm getting a few symptoms with a pressured feeling in the eyes, and would like to know whether TED could ever happen without Graves. There isn't a lot of info out there!


I have Graves and Hashi antibodies and TED. I am feeling better with T3 over range, but sometimes I feel my eyes are bulging more when Im over. It may be imagination. But Im almost 100% certain they are drier which maybe because the lids are not closing (more) than when on a lower dose.

Damned if I do, damned if I dont!

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Yes, I'm feeling better with mine over, too. But it's always a bit scary, feels naughty to do it ;)

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Ive always been a bit of a rebel ;)


Heehee :)


Thanks BB. Unfortunately over here in the UK trying to get a private Endo and an NHS GP to communicate is not easy so i often feel pretty much on my own in terms of day to day management.

Good to hear that you feel like you are emerging from deep hibernation - i really hope i experience the same at some stage.



T3 is exceptionally powerful for such a little pill.

When I first introduced 5mcg T3 a day to my T4, I experienced an inner heat & headache for three days & nights. Other members have complained of similar issues.

After that things improved & I increased my dose each week until I reached 20mcg T3. This was multi dosed initially three times a day, decreasing to twice after several months, so reducing the rapidity of onset and prolonging the duration of its action.

All my hypo systems improved, some overnight, some took months and I heavily supported my adrenal glands. Adrenal glands can become compromised through long term low thyroid hormone & and anxiety is a classic symptom. Elevated or low cortisol levels can impair good thyroid hormone function and effect blood sugar levels.

Your T4 was previously high so think you are wise to reduce when introducing T3. Especially if you are planning to increase T3 dose to 10mcg a day. Ask your GP to retest in six weeks & post results complete with ranges (numbers in brackets) for members to comment.

Good luck on your journey.


Adrenal & Thyroid Connection



Thanks for your help, can i ask how you supported your adrenals? I had a short synacthen test on my adrenals a couple of years ago it it was borderline so some support might be sensible.


Hello trademole,

I suspect the the ‘reaction’ you’re having is actually the reduction in levothyroxine.

As you’ve lowered your dosage by 25mcg’s your already low FT3 will now be even lower which will be making you feel awful. A drop in levothyroxine can be felt after a few days.

When the FT3 drops too low the body has no choice than to increase adrenaline as a safety mechanism. Your symptoms would certainly correspond to adrenaline.

I doubt that the very small amount of T3 that you’ve taken ie 2.5 mcgs x 2 would be enough to provoke a substantial response.

I am secondary hypothyroid too and it is much trickier to treat. I would go as far as saying it is a completely different ball game.

Central hypothyroidism tends to respond to much higher doses of medication than primary hypothyroidism. Your symptoms are probably very extreme in accordance with central hypothyroidism. You will also be a poor converter of T4 to T3 because of the suppressed TSH which plays a role in conversion.

I am currently taking

125mcgs levo and 20mcgs T3

I am by no means well yet. Much better than I was but still struggling.

Being central/ secondary hypothyroid you will also probably feel better with your FT3 higher in range. Some central hypos need it close to the top of the range. Some need both FT4 and FT3 close to the top of the range.

On a positive note I would suggest you’re moving in the right direction. You’ve got your FT4 high and now you’re addressing your FT3. Lowering your FT4 was I suggest the right thing to do. If you’re not converting it then it could make you feel pretty dreadful. The upper third of the range would be a good place to aim for with FT4.

You just need to get the T3 in now to raise your FT3 to a similar place in its range.

Once you get that FT3 higher you should start to feel better. Do it slowly though. My endo does no more than 5mcgs of T3 every 4 weeks. This allows the adrenals to catch up a bit.

Hope this is helpful.


Yes, very helpful thank you.


I was on 3 grains of NDT per day. I swapped for 1 x NDT early morning + 12.5 T3 and in the afternoon another 12.5 T3. I altered my dose in one day.

Although my FT3 was well over the top range with NDT I was still felling tired and foggy headed.

The reduction in the NDT and adding T3 has made me so well I am grateful for all of the advice on this wonderful site.

It does take time and patience but you will make it mostly with trial and error information on this site.

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Sounds like a great result for you! I agree with the helpfulness and knowledge of the people on this forum - way in advance of my GP and private Endo.


To answer your main question - can people have a reaction to T3, the answer is yes. It's quite common to have a racing heart, hot temperature, speeded up kind of reaction to taking T3 for the first time.

This is usually said to be an issue with the adrenal system. So you could read up about adrenal fatigue and how to support adrenals. Unfortunately the NHS doesn't recognise this mild form of adrenal issue, they only acknowledge the more extreme form of adrenal collapse, so you will have to self medicate if you want to treat this.

In terms of the dosing, you can start very low and build up slowly. As you felt fine after your morning dose, perhaps stick with just that for several days. Then try introducing the afternoon dose again. If it's fine, carry on. If you feel racy again, wait another few days before trying again. Once you're stable in those two doses, try increasing the morning one, and carry on until eventually you've reached the prescribed dose.

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Thanks for your helpful input. I think my adrenals are ok, i had a short synacthen test a couple of years ago which came back slightly subnormal but a trial of Hydrocortisone didnt make any difference.

I will persevere with the step by step approach you outlined.


Tests like the short synacthen test are checking for adrenal insufficiency or Addisons which is at the total breakdown end of the spectrum and is fairly uncommon in hypothyroid patients.

Unfortunately the NHS system States that someone either has a very serious condition like Addisons, or they are completely healthy, with nothing in-between. Adrenal fatigue is a term for the in-between, adrenals that are struggling but are not completely in breakdown. If you were borderline for the NHS test you will almost certainly find you have some kind of adrenal fatigue.

Although you may also find that once you are stable on T3 your adrenals will benefit enormously and won't be an issue. Unfortunately the issue you describe of struggling to get started on T3 is mentioned often on the forum, but the treatments aren't mentioned as often, and I think people go off and research on their own. So I don't know too much about the options available.


Oops, forgot to say, the preferred test for adrenal fatigue is the 24 hour saliva test. Usually 4 measurements but one of the companies is now offering 5. This is the first step if you want to look into it. Both Genova and Medichecks do a mail order kit I think. ThyroidUK website has the details.


Thanks SA, what are the best remedies for adrenal fatigue? Im getting quite into meditation/mindfulness as a way of reducing stress but interested to learn other supportive practices.


I believe Mindfulness is very good for it. But I don't know enough to give you a good outline. It's not often discussed in detail on the forum. Overall treatment will depend if you've got high or low levels - it tends to run high for a long time while you're ill, but then drop as the adrenals can't manage to keep up.

There are several herbs that help, things under the heading of adaptogens, and adrenal extracts.

A search of the forum might turn things up. Or maybe start a new post asking for pointers. I'd be interested to hear what you find out.


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