Thyroid UK
84,346 members99,345 posts

Need a bit of help understanding the T4/T3 thing please

Sorry I know I'm becoming a pain but now I've decided self treatment is my only option I just wondered if I could get a bit of advice.

I now know thanks to you guys where I can source various medications but I'm trying to decide which route to take.

At the moment my FT4 level is about as low as it can be without going out of range and my FT3 level is just below mid range.

I understand that the majority of meds contain both hormones but I've also read (if I've understood it correctly) that by taking the combination meds it tends to lower FT4 and increase FT3?

I'm just thinking if I start taking NDT or something similar is it likely to lower my FT4 more or will it increase because it's so low anyway.

The other option I'm looking at is just trying Levothyroxine as my antibodies are currently negative and I'm just wondering if I need a boost in my T4 levels. I've been on antidepressants for years and I've also been reading how that can damage/contribute to thyroid conditions!!

Sorry for all the questions just trying to get my head round it all!


3 Replies

Taking NDT, which contains both T4 and T3, does not lower T4, but the FT4 usually is lowish because you don't need as much - after all, if you buy your bread ready-made, you don't need to keep as much flour in the house, do you. The body only hangs on to the T4 it needs, and it doesn't need as much as if you're on T4 only.

When taking T3 in any shape or form, the FT4 is unimportant. It's the FT3 that is the most important number.

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Thanks greygoose :)

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Taking Levothyroxine which is T4 only or taking NDT which is T4+T3 will raise low FT4. FT3 is probably high because of high TSH stimulating conversion. Why not start with Levothyroxine which will raise FT4 and enable better conversion of T4 to T3. If after 6 months you feel Levothyroxine isn't helping you can always add T3 or switch to NDT.


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