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Thyroid UK
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Advice re: taking T3 and Levo please

Hi everyone, I am taking T3, which I have purchased, (my GP is aware and has agreed to monitor my bloods) and GP prescribed Levothyroxine. I'm reading conflicting reports of 25 mcgs T3 equivalence to 100 mcgs of Levothyroxine, some say 25mcgs of T3 equals 100 mcgs of Levothyroxine, others it's 25mcgs of T3 equals 75 mcgs of Levothyroxine. Could anyone advise me please? I know it's not an exact science but people's experiences and their ratios of T3 to Levo would be helpful. I was prescribed 125 mcgs Levo, I reduced to 25 mcgs and added in, (slowly and in stages), T3, I currently take approx 31.25 mcgs of T3 to 25 mcgs of Levo, I feel I need to increase. I feel ok but I want clarification if possible. Energy levels up and improved alertness but not massively. I believe based on previous tests that I have a problem with conversion to T3 but I still want Levo as I seem to be able to convert some to T3. Thanks, sorry for long post 😊

3 Replies

I don't think there's an accurate answer to this AngMaria . I've seen it said T3 is equivalent to 3x, 4x and even 5x Levo

Something else to factor in is the difference between brands. I was using 31.25mcg Unipharma T3 and did a straight swap over to Grossman Cynomel - big mistake!!! I have found Cynomel to be stronger than Unipharma.

I also need some Levo. I was taking 100mcg Levo with my T3, tried reducing to 75mcg and my FT4 plummeted from around 19 to 12.8 and I was very unwell so had to increase the Levo back to 100mcg and eventually things settled down again. Now just have to find the right dose of Cynomel!


I always assume 25mcg of T3 is equal to 100mcg because there are several T3s and it depends upon how the patient absorbs one or the other.

This is from Research re combo T4/T3 and go to page 80 and it was found that 3:1 combination was best.


This may be helpful:




T3 is 3 x stronger than Levothyroxine so 25mcg T3 is equivalent to 75mcg Levothyroxine. ncbi.nlm.nih.gov/pubmed/204...

There is no T3 to T4 ratio required. Adding a small amount of T3 to Levothyroxine is usually sufficient to overcome poor conversion. There's no need to take all or mostly all T3.


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