Any advice re Levothyroxine please?

Had bloods last week and was FT4 13 put on 20mg Carbimazole down from 40mg to block and 100mg Levothyroxine to replace. Liver had a bad day and so have another bloods. FT4 gone up o 14.6 in 3 days of above doses.

Last time we went from 40mg to 20mg I went up from 6.7 to 28 FT4 in 3 weeks, at this time was not taking levothyroxine.

My Doctor has said reduce levothyroxine down to 75mg which start tomorrow.

I am not sure dropping from 40mg to 20mg is sensible and want to take 30mg for a while to keep the block up.

Thoughts advise experience of this please? many thanks


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9 Replies

  • Roderick_0707,

    Liver problems are likely to be due to Carbimazole so you may be better off taking the 20mg prescribed and reducing Levothyroxine to 75mcg as your GP advised.

    Not many members are on block and replace so you may not get many replies.

  • Thanks Clutter for that, does reducing Levothyroxine get the free T4 used up? or is it Carbimazole that does that?

  • Roderick_0707,

    The Carbimazole stops you producing any T4. Levothyroxine is replacement T4 so as 100mcg is too much you need a reduced dose of 75mcg.

  • Thats great so what happens to free T4 in blood? would help me to understand what happens. A when on Carbimazole only FT4 came down from 44 to 6.7, how did it do this? does body use it or expel it? thanks for your responses, very helpful

  • Roderick_0707,

    Carbimazole blocked the production of T4 so there was no more natural T4 adding to the high level which was used by the body to convert to T3 and expelled in the normal way in urine and faeces.

    Your natural T4 production is now blocked by Carbimazole and 75mcg Levothyroxine replaces the T4 you need as 100mcg was too much. The 75mcg T4 will convert to T3 which is the active thyroid hormone in the same way as your natural T4 converted to T3.

  • Thanks Clutter as it was free and not bound with a protein did not know it would be 'used up' in converting to T3. Thats very helpful and thank you for your time

  • Just another thought Clutter, 3 days of 20mg saw my T4 creeping up from 13 to 14.6 which indicates it would keep rising as it did before, when it went from 6.7 to 28 on 20mg over 4 weeks. Will this get used up with 75mg levo or do I need to get Doc to increase to 30mg? thanks again

  • Roderick_07,

    It takes time for Carbimazole to stop production and it's also a question of balancing the Carbimazole and Levothyroxine doses. If you reduce Levothyroxine to 75mcg and raise Carbimazole to 30mg at the same time you are likely to develop hypothyroid symptoms as T4 may drop too low. You need to wait 6-8 weeks after Levothyroxine dose was reduced until your next blood test to see whether further adjustment is required. Of course, if you feel that you have become overactive in the meantime you should go back to your GP.

  • thanks Clutter now I feel educated enough, appreciate your time and knowledge. I will stay at 20mg and have bloods in 3 weeks which would be 4 weeks the Endo asked for.

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