Thyroid UK
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Starting trial of T3 tomorrow

I am finally starting a trial for T3 tomorrow, my Specialist is completely replacing my 175 micrograms of T4 once a day with 10 micrograms of T3 three times a day, I have tried to work out if this is about the same relative dose or less than I getting at the moment. I have a conversion problem so I am able to use about 40 per cent of the T4

that I am getting at the moment. My maths is very shaky can anyone please give me advice as to if I am getting an good exchange rate or if I am being put on a relatively

lower level of the hard stuff.

Thank you,

Kipper 2

3 Replies

Although liothyronine is four to five times as potent when measured in the blood it is only three times as potent as levothyroxine in tablet form. So you will be on a lower dose. This might be OK as you are not responding to levothyroxine. It is highly unlikely you are not converting as if this were so you fT3 would be low and your fT4 and TSH would be high. However, this is a pedantic point and it doesn't mean you might not respond better to T3.

Has your doctor told you how to migrate across to the liothyronine? Given the short half life of T3 I would stop the T4 and take about 10 mcg T3 daily after three days, 20 mcg daily after a week and 30 mcg daily after two weeks. This is just a rough calculation which will keep your hormone levels fairly stable.

Do you have blood test results from when you were diagnosed and recent results?


I was on T4 of 23.00 pico moles range ( 11 to 19.8) TSH 0.03

T3 4.5 pico moles range (3.5 to 6.5) . I have been on T4 for about 15 years

Thank you Jmh111 your reply has helped but if my place on the ranges help you to

give me a little more information I would be very grateful. I have been fighting for years for this but now I feel a little nervous. i was expecting to be on a mixture of T4 and T3 but I am to change to just T3.



yes I am surprised that you weren't put on a combination of T4/T3 to start with.

T4 stays in your system for 7 days where as T3 for only 1 day.

I am finding since I have gone to less T3 (with T4 as well) that I am feeling very fatigued from the middle of the day until the next morning until I have my tablets,so it's a fine balancing act.


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