Thyroid UK
84,236 members99,234 posts

How much difference does a dose of T3 make?

Having been on T3 for 12 months now, I'm near to having established the right dose, but I'm still making the final adjustments.

What I'm wondering, is how much difference one dose of T3 makes. I'm currently taking 6.25mcg in the morning, and the same at night. Before a blood test, I take my night dose, but not my morning dose.

Does anyone have any idea how much my morning dose would push up the FT3 result? I'm wondering where the real level might be within a couple of hours of each dose, as it will obviously give me a better idea of where my maximum level is.

I'm trying to avoid getting a blood test result any higher than necessary (to avoid having another argument at the hospital), so I don't want to take the morning dose just to find out, but my latest result was only 4.5 (I think the scale is 3.5-6.5).

I'm aware, of course, that how I feel is the most important thing, but that's another discussion, and all I'm asking is a theoretical question. Thanks!

3 Replies

I Just take one daily dose of T3 when I get up.

A morning dose would push up the T3 result if you are having a blood test that morning..

The advice is, if you take a bedtime dose to miss this and take it after the blood which should be at the earliest. You should also miss the morning dose and take after bood test.

You are taking an extremely small dose, a half of a 25mcg tablet? which is equal to around 50 mcg of T4.

I cannot say how high it goes but I know when I mistakenly took mine before a blood test, the GP was in a bit of a panic as I entered the surgery but I quickly explained and he was nice enough to give me another blood test and, believe me, I've never made that mistake again. :)


I don't think enough research has ever been done on the subject for anyone to be able to answer your question. The recommended time-gap between the last dose of T3 and the test is 12 hours. Any less and the level will rise - any more and it will go down - but I doubt anybody is capable of saying by how much. And, in any case, it probably depends on a lot more than we actually know about.



The biological half-life of T4 is approximately seven days and T3 about twenty-four hours. Because of the rapidity of T3 onset that achieves peak serum concentration, this causes wide fluctuations in the usual TFT's that doctors falsely govern med doses on.

A single dose of T3 (taken on an empty stomach) is rapidly absorbed and reaches peak circulating concentration in about two to three hours after ingestion but blood serum concentrations may remain elevated for six - eight hours.

After this time, blood serum concentrations start to decline, unless another dose of T3 is taken. ( Hence many members multi dose). Also because T3 arrives so quickly ( in the body) it's effect on the pituitary gland reduces TSH and most doctors ( who don't understand T3 psychology) won't like a suppressed TSH.

You are still on quite a small dose of T3. Not enough T3 ( when you need it) will further distort blood results when combined with T4 as the reduced TSH lowers the T4- T3 conversion. Therefore, a low T4 result should not be a problem when sufficient T3 is medicated.

When I medicated T3//T4 combo, I felt better on 20mcg T3 split into two or three times a day.

TFT's are only representative of what is within the blood stream and could be misleading when considering actual cellular activity. You would be better assessing thyroid hormone levels by combining blood results with how you are feeling. Some members find taking pulse and temps to be useful tools to see progress..


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