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Thyroid UK
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How do you know if you need T3

A general question really as I don't think I need T3 but theres a lot of talk about it. My doctor said the testing of T3 is difficult as it's like testing grains of sand (meaning it's not accurate)....so what symptoms do you look out for ?

How do you know if you need a higher dose of T4 or if you should be adding T3 to the mix?

This is just for info rather than specific requirement.

Cheers people, hope you are all having a good weekend....I'm enjoying the rugby xx

6 Replies

I think your doctor is wrong about the complexity of testing FT3, it's been successfully used for about 50 years. He probably means that it is more expensive than testing TSH and FT4.

If symptoms haven't been resolved by increasing dose of T4, TSH is in range and FT4 low in range, it could indicate conversion problems. Below or low in range FT3 would confirm this. At some point, I imagine someone will do a cost benefit analysis of the cost of FT3 testing vs 'guesstimating' T3 supplementation is required, T3 being astronomically expensive via NHS.

I'm surgically hypothyroid and became increasingly ill on T4 monotherapy, being over-replaced to suppress TSH post ThyCa to prevent recurrence. Adding T3 cleared brain fog & improved mental clarity but didn't resolve my increasing physical symptoms. Nor did 2 months of T3 solus. In the end I stopped all meds to allow any toxic build up to clear. That worked, and I've been able to tolerate T4 with T3 calming the palpitations and tremors I experience on T4 only.


I was on levo alone and felt dreadful. I was given the addition of T3 and it made a great difference to my wellbeing. Thyroid hormones affect everyone differently.

We can live without T4 but cannot without T3. T3 (liothyronine) is the active hormone that levothyroxine should convert to enough T3 but, as Clutter says, that doesn't always happen. The brain contains the most T3 cells.


Good grief, don't they come up with some bullsh%t to cover up for the fact they have no idea what they are talking about!?!

I agree with clutter, they just don't want to pay for it!


If you feel well on T4 you don't need T3. I started T3 when it felt like life had ended on T4 and it wasn't working anymore. I think if you're asking the question, and enjoying the rugby :) you don't need T3. T3 is more difficult to manage in my experience, so don't take it till you have to.

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Many thanks all....I was curious more than anything. Aurealis...you are right I am feeling good, well better than I've felt in a while. A few niggles but nothing like some poor souls on here.


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Hi The only safe way is blood tests, always TSH, T4 and FT3. may be on line, I use Blue Horizon, main site, well known lab.Finger prick on there is well tested and good. All DIY

Normally speaking T4 needs to be only in the top third of range but most people need FT3 to be near the top, never over. A lot of people need T4 and T3 together. If T4 is higher than this, chances are FT3 is too low and not converting. enough. Retest after 4-6 weeks on an low amount of T3 and possibly less T4, depends on the tests.



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