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Thyroid UK
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Help with free t3 and free t4 levels

I had a baby 9 months ago and since then have felt terrible physically and mentally. Have had an awful time losing weight despite exercise and eating well, terrible constant muscular pains, depression from having no energy and low temperature. My doctor started me on T3 only almost two months ago, thinking it would help both my depression and low free t3. Currently I take 18mg's of generic cytomel (t3) a day. My labs prior to starting the t3 were

TSH 2.0,

free t4 .8 (.9-1.8)

free t3 2.5 (2.3-4.2)

Anyway, last week I had my thyroid labs tested (did not take t3 the morning of testing) and TSH has gone down to 1.3, but free t4 is now lower at .7 (.9- 1.8) and free t3 is still on the lower side, exactly where it was before, at 2.5 (2.3 - 4.2).

Now my doctor wants to start me on Synthroid (t4), because if anything, my symptoms have gotten more severe, despite being on Cytomel (t3). She wants to add 50mcg of Synthroid. I agree that I need to get my free t4 up in order to feel better, but my question is, how much lower will my TSH go with the addition of 50mg of Synthroid? Shouldn't I start with 25mcg and see how my numbers look? Or will that not increase my free t4 enough to make a difference? And why has my t3 level remained the same despite being on t3 the last two months?

11 Replies

For a start results are read differently if you are taking T3 in any form. The TSH should be suppressed, FT4 can drop down to halfway in its range but FT3 should be high in its range which yours isn't. Why your FT3 has risen I have no idea but suggests something else isn't quite right. Are you taking your meds on an empty stomach with a full glass of water to make sure they go to where you want them. Then no food other than water for an hour and also keeping other medication 3 hours away and Vit D, Calcium and anything containing oestrogen 4 hours away. PPI's should also be 4 hours away as well though it's not a good thing to be taking if you are a thyroid patient. We tend to be low on stomach acid and PPI's deplete it further so we may not be breaking down the. Onnents of our stomach correctly so not getting correct dose of our medication and harming nutrition as well.

Your labs prior to starting T3 show that you were very undermedicated. The aim is to get FT4 and FT3 in the top third or even the top quarter of their respective ranges. Both or rock bottom and needed to be raised. It's looks like your doctor hasn't a clue as those results are so low and your later results she doesn't know how to read. Is there someone else you can see?


We usually have T3 prescribed in mcg. So I'm not sure what 18mg is equal to in mcgs. Hopefully, someone will answer that question.

The blood tests used were introduced along with levothyroxine alone, so they cannot equate when we take T3 only.

T3 lowers T4 and can suppress the TSH. I think your dose of T3 may be on the low side and that's why you don't feel so good.

As our own thyroid gland isn't producing T4, (which has to convert to T3) we won't have a T4 that 'fits' into the ranges (which I said were for taking levothyroxine alone).

Two months on liothryonine at the same dose is unusual as it is usually increased until we are symptom free i.e. we feel well with relief of clinical symptoms.

I take 50mcg myself. Some doctors are nervous about T3 and don't understand much about it.

Your clinical symptoms are hypothyroid so I don't think you've been given sufficient dose.

The fact that your FT3 is low and hasn't risen, suggests you aren't on sufficient due to no increase.

Your doctor is correct about T3 helping depression but you have to have an adequate dose. I know someone who took 150mcg in order to function.

You need T3 increased until you have relief of symptoms. As it is the only Active hormone it goes directly into our T3 receptor cells and its work then begins and lasts between one to three days.



88mg would be 88000 micrograms. That is ludicrous so I would assume a typo or other simple mistake.


Thanks - a misreading by me. What is 18mg please :)

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It would be 18000 micrograms! But 18 micrograms can only be approximated as three-quarters of a 25 microgram tablet.


Pitiful but thanks for leading me to the correct equation.

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Your dose of T3 is 18 micrograms and can only be approximated. (i would guess about 75mcg of levothyroxine ) and is too low).

Usually T3 is in 25mcg tablets which is approx to 100mcg of levothyroxine. I myself take 50mcg.

We are all individuals and doses vary between each person but your T3 dose is too low. Your GP could add T4 but also keep you on T3, as research has shown that a combination dose can work well.

Too low a dose of thyroid hormones can backfire and make us feel worse.

T3 at optimum would/should relieve pain.


As others are saying, this is a pretty low dose of T3. The logical thing is to raise it, then rest again in 6 weeks and adjust again. The simplest explanation for why freeT3 hasn't increased is that the dose is too low to shift it. Although in my experience if you increase and test, increase and test, several times in a row, the freeT3 doesn't always raise corresponding with increases. In my case I don't know why, but it may be very sensitive to external factors like what you've eaten and how much activity you've done.

You don't actually need to raise your freeT4 to get better. T4 is only a storage hormone and T3 is the active hormone. Ideally you want your TSH at one or below it - many people need the TSH completely suppressed to be well. Your most important number is freeT3, and you want it in the top third of the range.

Ideally you should continue with the same treatment for 6months or so, ideally having blood tests and does adjustments every 6 weeks. If you don't see improvement in that time, you can turn try a different treatment (e. g. Adding T4). If you don't give it a good trial, you won't know if T3 can work for you. It's quite common to give up just because an initial dose is too low.


T3 is only going to help if you take enough of it! 18 mcg is a very small dose. I don't know whether you need to add T4 or not - it's a storage hormone. Is a storage hormone going to make you feel better? Depends on how well you can convert it. But, plenty of us live very well without T4. I do. But, I need to take a lot more than 18 mcg T3! Ask her to increase your T3, first, I would.


Thanks for the replies.

I guess my doctor's line of thinking is if my t4 increases, my body will then be able to convert a higher level of free t4 to free t3, and bring it up that way, instead of increasing the t3. I think i am able to convert. I was just started on t3 to help with the depression too.

Strange thing is, if I take 25mcg of t3 I get exceptionally hungry and don't feel well. It's odd that on 18mcg I don't have this feeling.

I also had my free t3 level measured after taking my 25mcg dose and it was 5.4 (2.3-4.2). It explained why I was feeling kinda hyper. So I lowered it to 18mcg, had my levels tested without taking t3 and levels were 2.5.

Is it possible adding t4 could help get my free t3 up since apparently I have a hard time doing it with t3?


I should also add that I am adding the t4 to the t3 because I hope to have another baby in the next few months, and t4 is very critical in having a healthy baby, more so than t3. So I'm hopping to get my levels up of t4, at the same time raising free t4 and free t3.


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