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Thyroid UK
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When will T3 kick in ?

Hello all 🤗

Have been on T3 for 3 weeks , prescribed by my doctor, and am up to 12.5mcg daily.

Apart from a sort of jittery feeling on some days, I haven’t really noticed any benefit.

I know everyone is different, but can anyone tell me how long it might take for me to feel it helping as I still have no energy increase.

And how long should I be taking it before I retest my levels?

Many thanks x

9 Replies


You should retest 6 weeks after a change in dose (I have found that I need 8 weeks to feel the full benefit and for my results to stabilise).

Everyone is different. When I started adding T3 to my Levo I didn't feel anything at all, I increased gradually, tweaked both Levo and T3 for quite a while and eventually realised that I was feeling better than I did. It showed in my results before I felt it really. I never had a moment of "Wow! I can really feel the difference T3 has made" like some people do.


Susie thank you 🙏. You’ve made me feel SO much better. I have been waiting for that ‘lightbulb ‘ moment that people talk about and was wondering why I hadn’t had that feeling yet.

I am more than happy to wait and sit it out and maybe, like you say, gradually realise I suddenly feel better.

Susie, you and the team, are real heroines on a daily basis, for the way you all devote your time and energies to all of us.

Forever grateful, xx


You are welcome, and you are very kind :)

Just checking - your vitamins and minerals are optimal aren't they? You probably know that is needed to help thyroid hormone to work properly.


Yes, all optimal. I’ve been taking everything that was kindly recommended to me, for months now , but never felt any real improvement , but take them all daily, without fail.

1 like

I felt the difference, though only temporary, within hours with adding T3 initially as tiny 3.12 mcg dose, though slowly over following month or so got up to 25 mcg. I was stuck 24/7 on my sofa over winter and now walking 10,000 steps daily but still falling asleep in the afternoon, some pain, hair falling out ( tho that can be the T3 itself), no weight loss etc. So better but some way to go- certainly felt hypo again last week when up north it got relatively cool again and I was back in my winter coat, socks, 2 layers and blanket!

1 like

Thanks Judith,

I’m glad it’s working for you.

I know I need to persevere and hope it may kick in soon.

I’m still stuck on the sofa, despite this beautiful weather, but just haven’t got the energy to be bothered .

Can’t wait to be able to do 10,000 steps.

I used to love walking, but these days can barely get out of bed !

Hope the warm weather has warmed you up a little . 😘


Many thanks. Have you not got an option to add tiny bit more T3 as it sounds as the 12.5 mcg dose isn't enough, or are you stuck in doctor's timetable re blood testing?


He thought I might get palpitations if I put it up to 25 mcg. But I’ll wait another 3 weeks and then test. He’s a private dr and fairly flexible. He says he wants my level to be at 6.0, it’s 4 at the moment, so I know he’ll put it up.

I’ll just have to take it slow, as we all seem to have to do.

Where abouts ‘ up north ‘ were you?

I’m from Leeds originally but live in Wiltshire now . ( definitely warmer than Leeds ! )😂


Ok, if you have a doctor you trust, better to be reticent about introducing T3 than gung-ho. I swopped Wiltshire / Bristol for Cumbria! But very warm and dry up here at mo.


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