How Long Should wait after taking t3 for test?

Hi All,

on 23rd of december i had my free t3 tested, it was FREE T3 6.3 [3.1-6.8]

I took t3 for 2 weeks to see if it raised my body temp

I got it tested again 3 days after my last pill and it came in 4.9 [3.1-6.8]

Is it possible I didn't wait long enough for my own thyroid function to kick in again? The past few times in past when I had t3 tested, it was always right at top of range

note: I also started taking iodine ( 50mg day )

also, does this active b12 look low. I'm a 29 year old male

Active B12 57.6 [ 25.1 - 165.0 ] N

Last edited by

7 Replies

  • Sorry you have had no replies - hopefully someone with relevant knowledge will pick this up from Latest Activity...



  • T3 has a half life of about 8 hours. While not taking your normal dose on the morning of testing is correct, not taking it for 3 days means you have utilised any 'stored' T3 and would explain why your recent T3 result has dropped.

    I'm not sure whether supplementing iron when on thyroid meds is recommended or not. I was under the impression that thyroid hormone replacement should make it unnecessary to supplement with iodine.

    I think your B12 looks low. You shouldn't supplement without having your folate level checked first. I think supplementing B12 may mask low folate but it might be the other way around.

  • You do not say how much T3 you took. If it was not more than a physiological dose (the amount your body produces), then it is possible that you will not see any benefit. What can happen if that the T3 you take is detected by the body's control system, you then make less TSH which tells the thyroid to produce less thyroid hormones and the level of free T3 stays the same! Therefore your body temperature does not go up and you do not feel any better.

    Blood tests are not a good indicator of how the thyroid treatment is working - symptoms including body temperature are a much better indicator.

    Your free T3 is not at the low end of the range so you are probably not hypothyroid. Your symptoms could however indicate Thyroid Hormone Resistance. This is genetic and another indicator would be if you have close relations with similar symptoms.

  • I took 25mcg of T3, I'm waiting on my reverse T3 result and cortisol result. Then I will try again

  • Your free T3 is at the high end of the normal range so your thyroid appears to be working well so I am not sure what you mean by "my own thyroid function to kick in again". Similarly with your high levels of free T3, taking 25 mcg of T3 is simply replacing some of your own T3 and will not raise the level.

    It looks like the issue could be in relation to the T3 binding to the receptors. If you do another test of T3 monitor your basal temperature every day and this will give an indication if the T3 is doing anything.

  • Hi, yes my free t3 level is fine.. however I have a TSH of 6.33 but my ft4 is also at top end of range.. and with my low body temps, I thought taking a bit of t3 might help. I now realise 25mcg is not enough

  • When T3 is at the high end of the normal range you would expect TSH to be very low. Your high TSH is a very strong indicator of Thyroid Hormone Resistance. This runs in my family and I have pulled together information on it. If you want a copy send me a personal message with your email address and I will send it to you.

You may also like...