Thyroid UK
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T4 toxicosis

Was taking Levothyroxine 100 mcg for 10 years then started to get palpitations, missed beats and landed up in A&E with Atrial Fibrillation. Diagnosed with T4 toxicosis and taken off T4 for

short period where I immediately felt better. IBS I had had for years cleared up and I was less anxious. However my TSH

went up to 44!

Now seen by Endocrinologist who has prescribed 25mcg Levothyroxine and 10mcg T3 but still feel exhausted. Would I be better on NDT or does T3 take time to work?

3 Replies

I wonder if the culprit might be that your previous dose was too low i.e. 100mcg of levo caused AF. Were you absolutely clear of clinical symptoms for those ten years?

My personal opinion if you, after 10 years on 100mcg of levo and became toxicosis that levothyroxine might not suit you at all now. T3 works more or less instantly (I found that anyway when it was added to T4). (T4 did nothing for me).

Your new combination dose is only around 55mcg of levo which is probably because they are being cautious now. Are you being monitored about every 6 weeks with a small increase given?

You can always ask if you can take T3 only but you need to be carefully observed. whatever you are on.

I have read that some people can be very sensitive to levo, even at 5mcg.

The fact that you immediately began to feel better when T4 was withdrawn is a pointer (I think) that your body might be better off without it.

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"


Thanks for your comments.

I was symptom free for the ten years and I may be imagining it but it seemed that the first symptoms of hyper/toxicosis occurred when I went onto a gluten free diet.

The endocardologist has requested coeliac blood test plus TSH, F T3 and F T 4, but whatever the blood results I will go back on a gluten free diet and see if I feel better.

Am seeing him in 2 weeks and will discuss whether it's better for me to be on T3 only or NDT.


Going gluten free might have significantly reduced your need for replacement Levo.

Many people see large reduction in antibodies when following gluten free diet.

Lower antibodies might mean we need less T4.

Coeliac test can I think give false negative.

Others on here, I am sure, can tell you more


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