Thyroid UK
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How long does it take for T3 to come out of a persons system?

I'm asking because I'm on T3 only and I stopped the T3 for 48 hours and then had a blood test. My FT3 went down but my TSH was still low.

TSH 0.02 (0.27-4.2)

FT4 6.8 (12-22)

FT3 4.9 (3.1-6.8)

When I had a blood test when I was taking 60mcg of T3 only;

TSH 0.05

FT4 7.8

FT3 5.8

I didn't take any T3 for 24 hours before the test.

When I was on Levothyroxine;

my TSH was 2.14

FT4 16.9

and FT3 4.4

I know T3 only can give you funny blood tests but shouldn't the TSH go up after stopping the T3 for 48 hours, especially as the FT3 went down from 7.8 to 4.9?

Neeta x

7 Replies

Hi T3 at maximum in 6 weeks and so reverse is true. bet to not have a FT3 test having taken T3 as doubles it. 12 hours later , is usually fine, experience! T4, synthetic like wise takes about 4 weeks, but best not taken on the morning of the test.

Vets have known this for years, most docs "not"



This is an explanation and read the whole of the 4th question:-

For someone taking 100 mcg of T3, we expect your pattern of lab results—a low TSH and high T3. However, your TSH and T3 levels are irrelevant to whether you're overstimulated or not. Two studies we just completed confirm other researchers findings: these tests are not reliable gauges of a patient's metabolic status. Many patients taking T3 have TSH and T3 levels like yours but still have severely low metabolic rates. Their metabolic rates become normal only when they increase their dosages further. Their metabolic rates become normal and they have no detectable overstimulation.


Do you know if there is a test for metabolic rate or does it just depend on how we are feeling?


Some doctors may do metabolic testing but, as far as I know, we can surmise by how we feel. No painful tissues, muscle, feeling unwell, fatigue etc. We should have no pain, insomnia or any other clinical symptoms, although some people feel much improved and don't mind if they're not 100%.

There is a whole lot of topics at the top of the page of the previous link which gives us lots of info, usually by patients asking questions and getting answers:-

This is another excerpt from from Dr Lowe who died last year:-

Troubled hypothyroid patients on T4-replacement often hear the same refrain from their conventional doctors: "Well, your TSH is in range. That means your aches, fatigue, mental fog, depression, and cold hands can't possibly have anything to do with your hypothyroidism."

I know from one of the studies I mentioned in the section above that this refrain is a false one. The TSH level is simply grossly unreliable for gauging whether the thyroid hormone product a patient is using, or the dose he or she is on, is working well for him or her. For too many patients, the product or dose is failing to provide the patient with normal metabolism, body temperature, brain and heart function, and relief of symptoms.


Thanks Shaws. That's very interesting.


TSH is very unreliable as a measure, keeping the TSH suppressed is usual for a lot of people, your doctor should be listening to you as you relate symptoms not looking at blood results.


Thanks for the replies.

Glynisrose the problem is my endo won't prescribe me T3 because it suppressed my TSH when I was on it. And I can't convince him that the TSH doesn't matter.


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