Thyroid UK


Hi could anyone explain ,when taking t3 only what happens to theTSH levels ,as I understand it, t3 affects the TSH level quickly.So when I go for TSH blood test at 0800 (not taking my early am dose ) the TSH level is whatever level it is,but if I took my t3 am dose it would be a lot less.So TSH level when taking t3 throughout day is different to the TSH level which is actually occurring.Hope this makes sense.

6 Replies

Susiebow, 40mcg T3 is likely to suppress TSH <0.03 in most people. Taking the dose before the blood draw probably won't affect TSH much but is likely to cause FT3 to shoot up.

The reason for leaving 24 hours between blood draw and last dose is to measure normal circulating hormone levels rather than the peaks caused by medication after recent ingestion. T3 is likely to be out of the bloodstream after 6 hours so 12 hours between last dose and blood draw is probably sufficient for someone on T3 only.

1 like

Hi Clutter I take 40 mcg spread throughout the day 20 10 and 10.Felt better in one way ,a bit brighter over last 3 days ,was up to 45 mcg but felt shaky and heart pounding hard ,gone back to 40 mcg.Still lethargic,but feel an improvement just hope lowering to 40 mcg will not make me worse again.


Susiebow, try raising to 45mcg again in a few days.


ok thanks clutter


Hi Clutter, I am on t3 only and take 80 at bedtime.. Last year I took only 40 the night before the test and the result was t3 15. something. In May this year I didn't take any the night before and my result was t3 5.9 so no t3 should really be taken for 24 hours before bloods, the dame as t4. Just a thought. xx


Even same


You may also like...