What usually happens to TSH and T# levels once a person starts taking T3 along with the T4?

My endo increased my dose of Synthroid in July to .137 and after doing labs in October again the results showed TSH levels were at .525 but my T3 levels hadn't budged from the bottom of the range. She started me on T3 5mcg in morning along with the Synthroid and 5 mcg T3 in afternoon. I feel somewhat better but am thinking my T3 dose isn't really enough to make the difference that is needed.

When adding the T3 does the TSH levels change too? I'm not exactly sure how it all works. Thanks for the feedback.

15 Replies

  • TSH =thyroid stimulating hormone from pituarity trying to kick a failing or failed thyroid into action on a feedback loop

    hence supply the body with either t4 which its supposed to convert to T3 or by supplying T3 itself in adequate amounts the feedback loop is satisfied

    And pituarity stops production

    sadly far too few docs and endos remember this very simple biological fact and bang on about cant have TSH suppressed much to the detriment of their patients

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  • The response of the pituitary in making TSH depends strongly on T3 levels in the blood. There are two possibilities. If you are keeping the same T4 dose, but add T3, then your FT3 will rise, FT4 may stay much the same but TSH will fall. If you are lowering T4 dose and then adding T3, your TSH may not fall but your FT4 will and your FT3 should rise - thus the ratio FT4/FT3 will be smaller than if you were taking T4 alone. - though the actual numbers will depend on how much T3 you are taking.

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  • The ratio of T4/T3 is best when it is in a 3:1 ration. As explained in the following link.

    Go to page 80 and read the top left-hand column. I know Endos titrate doses according to the TSH but I don't think that works best for patients. Low or suppressed TSH wont give us heart attacks etc.


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  • guysgram, sometimes other medical conditions put the kybosh on conversion of T4 to T3.

    Just as an example, and I'm not suggesting or implying that this is your situation: fatty liver would have an effect. Also fatty liver produces symptoms such as fatigue. Most of the T4 in the body is converted to T3 by the liver, so if there's a liver problem, then fT3 will not respond to higher T4 doses.

    I think your doctor is going about things the right way in that your Synthroid dose is not being lowered but a judicious amount of Cytomel (?) is being added. Your body may be 'adjusting itself' to the addition of T3 and reducing the amount of T4 it is converting to T3. Blood testing will show if this is the case.

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  • Guysgrams, 10mcg T3 is equivalent to 30mcg T4. Adding T3 to 137mcg should raise FT3 and reduce TSH. FT4 may also drop as oral T3 can stimulate better T4 to T3 conversion.


    I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.

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  • 'FT4 may also drop as oral T3 can stimulate better T4 to T3 conversion.'

    Not experience this at all. Is this factual or hypothetical?

  • Gabkad, I've read it, sorry no link to share, and I experienced it. FT4 dropped when T3 was added to Levothyroxine without adjusting Levothyroxine dose and FT3 rose.

  • Must be something wrong with me then.

    I've never had 'stellar' conversion. Records going back to the mid 80s. Probably genetic. Although saying that, up until I was in my teens, it was pretty obvious that the thyroid was working just fine. Something happened and it would never unhappen.

  • Gabkad, we all metabolise and convert differently. 'T3 can stimulate better T4 to T3 conversion' is a generalisation and doesn't mean it will stimulate better conversion in everyone.

  • Just asking the question since I just started adding T3 to my Synthroid.

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