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Thyroid UK
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Reduction of Carbimazole?

Hi Can anyone help with advice on reducing my carbimazole please? Diagnosed with GD and hyper from Feb. Carb started on 2nd March and propanolol a couple of weeks prior to that. Endo prescribed 30mg Carb a day which I then reduced to 20 mg per day on 22nd April because nearly all symptoms had stopped, apart from anxiety. My Bloods:

2/3/15 - FT318.6 (2.5-6.5), FT4 63.9 (8-21) TSH 0.01, Trab 21.

29/4/15 FT3 3.4, Ft4 11.8, TSH 1.33, Total IGA 2.56 (0.8-4) IGA 2.56 - coeliac test done as a precaution.

I've decided my GP is FAB!! I asked him about reducing the medication and he admitted h'es not sure and that I knew more than him but he wants to learn!

I asked for Vit D, B12 ferratin, folate and TRab again this morning and he's done them all, so results from them next week.

I'm not sure how much Carb to take now, I feel well but want to be optimal.

9 Replies

Cal123, you judged the reduction from 30mg to 20mg well. Make reductions slowly because the Carbimazole has brought your TSH up and FT4 and FT3 down, but you probably need to be on it longer, usually 6-12 months for it to re-regulate your thyroid. A dose decrease of 5mg might be okay as your FT3 and FT4 are quite low now. Have a blood test 4 weeks after adjusting dose.


Hi Clutter

thank you. I really don't want to go hypo and I was thinking about reducing it to 10mg now as the drop in the bloods has been quite sharp in a short space of time. do you think that would be too much?



Cal123, I really don't know enough about Carbimazole to advise. It seems a lot to me.


ok thank you Clutter. There is a debate about this at the moment as lots of GP's are starting people on too high a dose to start with rather than starting low and building up to avoid a hypo crash. I shall keep investigating :)


Hi Cal123

I was on a similar dosage to you my TSH isn't as good as yours and my endo has reduced my meds to 5mgs daily, I would have thought 20 was to high if you reduce it to 10 and see how you feel after your next blood test if you start to go hyper you can go up. You will soon learn your own body and what dosage works best for you.

With your results 20 would be too high

Good luck


I agree Elayneg. If I stay on 20mg then Ill end up hypo pretty soon. I've halved it to 10mg now and will then halve again to 5mg. I'm having to do this as my GP is not sure, but he's learning and pretty supportive. The hospital have messed up with my endo so not sure when I'm next having bloods, although I will demand GP does them if hospital don't sort out their mess. So, if I had not done my own research I would still be on 30mg a day and no doubt hypo .


Make sure you leave enough time between dose changes as I found I didnt really feel all the differences until after 6 weeks of being on the new dose.


I'm scared to leave that it long because if my levels drop at the speed they went up then I am going to be hypo soon. I don't have any hyper symptoms except anxiety .


You can titrate dose down to 5mg according to weight, symptoms & bloods.

You see the difference quickly with a hyper thyroid.

I waited for consultant appointment & went hypo.

I like to think of mine as a pet that costs a lot to feed!


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