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Thyroid UK
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Hello. I was on carbimazole to treat my overactive thyroid. I read that I was meant to be on it for 18 months. However, I was taking it for 18 years. I am wondering what this has done to me as my health is quite poor. (The thyroid was eventually dosed with radioactivity and I'm now on levothyroxin.) Has anyone any information about carbimazole when taken for much longer than usual? Thank you. Timon.

2 Replies


There's no reason why Carbimazole shouldn't be taken for decades if required. Any adverse reactions will usually manifest during the first few months of taking it so people who don't want RAI or thyroidectomy can continue taking Carbimazole.


Doctors do not usually like patients on carbimazole long term because of the possibility of side effects but I can't find any research on long term health.

The side effects usually show up quite quickly - a rash, joint pains, fever, jaundice from liver damage and an effect on the bone marrow.

However, I've been told on numerous occasions that patients have been on carbimazole for many years without any ill effects.

What I would be looking at is your current thyroid test results. Your poor health could possibly be due to not being on enough levo or needing some T3. You would need to have ALL the thyroid tests done, though to check what your levels are.

Also, check side effects of any other meds you are on.


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