How many hrs is it best to leave between my last dose of T3 and getting my blood drawn the following morning at 8.30am?

I am currently taking 43.75mcgs of t3 only and multi dose throughout the day, the largest dose being 25mcgs first thing of a morning then topped up throughout the day at 11.30, 2.30 and with my last dose of 6.25mcgs being at about 6pm. Is it best to miss this last dose?


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8 Replies

  • Hi Pink. It's probably up to what you want to achieve. When people on Levo don't want their dose reduced which often happens within the NHS, it's important not to show a lowered TSH which may happen shortly after medicating. But is that likely to happen when you are only taking T3? If your T3 reading is very high, will your GP or Endo take away some of your T3. If that's not a worry I would think you could do what you normally do. Personally , since it is such a crucial reading, I think I would prefer getting the real reading by doing what I normally do.

    Possibly it would be best to wait till the blood draw in the morning to take your first dose since you may get an unusually high reading within a couple of hours after taking. It is just my opinion as there has not been much information about T3 only.

  • Its not a case of just not wanting Levo reduced. Your levels spike showing an inaccurate reading if you take it too close to getting bloods drawn, which can then result in levo being reduced when it shouldnt be.

  • You are quite correct, of course. Taking it before blood is drawn will result in a spike of T4 and lowered TSH, giving unrepresentative readings, and doctors won't take this into account. Unfortunately many doctors don't seem to realise how important this is and people end up with their dose being lowered unnecessarily :( I think that's the point Heloise was trying to make :)

    Carolyn x

  • I'm not entirely sure, but I would have thought that such a small dose more than 12 hours before the blood is drawn shouldn't cause too much of a problem. I'm not sure though. Hopefully someone else will be able to give a more definite answer for you :)

  • T³ has a half life of approx 8 hours so you should be fine to take your evening dose.

  • I'm curious to know how you manage such an exact dose? I'm only on 10mcgs T3, with some accompanying Levo. The Endo wanted me to take 5mcgs T3 in the morning and 5mcgms in the evening, but trying to split a small 20mcg tablet into 4 resulted in a pile of crumbs! The pharmacy said it only comes in 20 mcg tabs. Are they wrong?


  • Hi Pink

    I have some experience of this and think I can help.

    In August I was taking a single dose of 30mcg T3 at 6am ish. I then had blood tests done THE FOLLOWING DAY at 11am - RESULTS TSH 0.28: fT3 3.7 : fT4 2.9

    The endo and GP thought I had taken my T3 the same morning - their verdict was that I was taking plenty as my TSH was in range AAAGH!

    The fT3 is below range and should have shown a spike as Suzymac says but they didn't want to know when I said I was undermedicated.

    If you can hang out I would take only your first dose on the day before or even just the last dose two days before.

    Re the 8 hour half life - true for T3 we believe BUT the enzymes which are created by the T3 last in the system longer so may influence results - see Dr John Lowe.


    Since my test I have increased to 31.25 in split dose plus 2 x NT and with adrenal support much much better, will post separately.

    Good Luck with your test results


  • You shouldn't take your T3 on day of the blood tests as it is the active hormone. Best taken the morning before and then straight after the test.

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