Thyroid UK
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Low T4 - ? need to adjust T4/T3 medication ratio

Blood Results 8/12/17 on Levothyroxine 100 mcg and Liothyronine 20mcg

Free T4 13.00 (9 -25)

TSH 0.05 no range given

Free T3 4.4 ( 3.5 -6.5)

Liothyronine increased to 30 mcg on 9/1/18

Blood results on 16/3/18 - advised to repeat bloods 2 months after increased dose

Free T4 13 (9-25)

TSH < 0.05

Free T3 5.2 (3.5 -6.5)

I had understood that once treated TSH level becomes irrelevant but have seen comments on this forum that having TSH within range helps with T4 conversion. I also saw a comment by someone saying she felt better with T4 in upper end of range even when T3 was good.

I have been hypothyroid for 24 years. About 8 years ago I had T3 added by an endocrinologist and it was a major breakthrough for me. I had assumed that I had autoimmune thyroid disease but the only time I have antibodies tested was last December when they were normal but wasn't sure of significance of this so long after initial diagnosis ( my thyroid gland is almost non existent on ultrasound).

I have a very supportive GP so when I started to feel symptomatic again she agreed to increase my T3. At the same time I have been addressing my vitamin levels and they are improving with supplementation. My symptoms have improved with the increased dose of T3 but I still don't feel as alert and have as much energy as I have done previously. Of course I am getting older all the time which may be relevant!

My T3 is now in upper end of range but my T4 is still at bottom of range . I am wondering if I am still able convert some T4 to T3 and if this might be improving with better vitamin levels. In that case might it have been better to increase the levo rather that the liothyronine? I realise this might be a case of trial and error but would value any comments.

I did post on the same subject a few days ago but didn't get much response so I'm trying again. I have not included all the vitamin levels again in the interest of brevity. I'm see my GP next week and want to go well informed.

14 Replies

I think it’s more likely that you need an increase in T3 but GP may be unlikely to suggest this because of low TSH.

1 like


Have you got any old results for TSH/FT4/FT3 when you were on Levo only? That will tell us what your conversion was like and how likely it is that you will convert some of the Levo to T3 if you increased that dose.

I am on a combination and have done a lot of tweaking of doses over the last 2 years. Through experimenting I have found that a low FT4 makes me feel awful, I need mine over half way through the range with FT3 high in range. But we're all individual and have to find what suits us best through trial and error.

When taking T3, the TSH is going to be very low or suppressed, that's what it does, so it's unlikely you'll get your TSH back into range unless you lower your dose. My TSH was suppressed for over 20 years when on Levo alone.

I'm sorry you didn't get much response to your previous post, this forum moves very fast and it just depends who's around at the time as to who sees your post when it's near the top of the page.

I've taken your vitamin and mineral results from your previous post

Serum Vit D 102 nmol/L

The Vit D Council recommends a level of 100-150nmol/L and you've just about reached it. You now need to find your maintenance dose by trial and error, which may be 2000iu daily, maybe more or less, maybe less in summer than winter, it's trial and error so it's recommended to retest once or twice a year to keep within the recommended range. You can do this with a private fingerprick blood spot test with City Assays

I like to keep mine around 150nmol.

Are you taking D3's important cofactors Vit K2-MK7 and magnesium?


Serum vit B12 345 ng/L ( 2.6 - 700)

Are you supplementing? If not then I would suggest taking sublingual methylcobalamin lozenges, I would start with one bottle of 5000mcg then change to 1000mcg. Further testing will not give a baseline unless you leave off supplementing for 4-5 months, but can indicate if you are supplementing at the right dose.

An extract from the book, "Could it be B12?" by Sally M. Pacholok:

"We believe that the 'normal' serum B12 threshold needs to be raised from 200 pg/ml to at least 450 pg/ml because deficiencies begin to appear in the cerebrospinal fluid below 550".

"For brain and nervous system health and prevention of disease in older adults, serum B12 levels should be maintained near or above 1000 pg/ml."

When taking B12 we need a good quality B Complex to balance all the B vitamins. Don't bother going back on a multivitamin but a Complex would be the correct thing to take, make sure it contains methylfolate rather than folic acid, and it will contain some biotin as well.


Serum folate 15.1 ng/ml ( 2.6 - 17.3)

Folate should be at least half way through range, a high level is fine if B12 is good.


Serum ferritin 58ng/ml ( 10 - 420)

For thyroid hormone to work (that's our own as well as replacement hormone) ferritin needs to be at least 70, preferably half way through range. However, I have seen it said that 100-130 is best for females so I do think half way through your range might be too much. I see that you are taking an iron supplement, you could also start eating liver regularly which will help raise your level.


Thanks for this comprehensive reply, I really appreciate how much time you all put in to this. Unfortunately I don't have any old results. My GP surgery have changed to a new on line system which only gives results back to when they started with it unlike the old system which gave results going back years. I can ask next week but I know they often didn't do the FT3 back then. If I want to try and increase my FT4 do you think I should ask to increase the Levo and in that case should I carry on with 30mcg Lio or should it go back to 20. I realise it is going to be trial and error but it is interesting to hear that you have been through the same process and hopefully I can learn from your experience.

After these blood results I started with 1000 mcg sublingual Vit B12 tablets but found they took so long to dissolve I have now changed to a spray.I might get some 5000 mcg. I was a bit wary of going to far. I had upped my vit D to 3000iu between these 2 results but will go back to 1000iu when the sun comes out! I don't like liver but seem to be making progress with the iron supplement I am taking so shall carry on with that.

Thank you again.


Free T4 13 (9-25)

TSH < 0.05

Free T3 5.2 (3.5 -6.5)

If these were my results I would leave my T3 at 30mcg and increase Levo by 25mcg at the moment, retest in 6-8 weeks and see what difference it has made. Even if you have some conversion I doubt it will be enough to push your FT3 over range, and you have plenty of room for that to increase.


Thank you. I will see if my GP will go with that.


No, I don’t think your conversion would improve if you added more levo. You’d struggle to get the TSH up above 1.0 while taking 30mcg of liothyronine anyway - almost any amount of lio seems to suppress TSH.

I see you’ve done quite well to raise your ferritin levels from 15 to 53(?). Keep going on that one - ideally you want ferritin to be higher than that, as a rough guide higher than 70 for starters. But your B12 is 344(?) (sorry, doing the numbers from memory after a quick glance at your last post), and I’d say there’s still room for improvement there.

Symptoms do lag behind dose increases unfortunately, so you may well see improvements in the next few weeks without raising your dose anymore. There probably is wiggle room though for a touch more liothyronine, maybe another 5mcg or so.


Thank you for this. It's not straight forward is it? Perhaps I need to be a bit patient and see what further improving my vitamins does for my symptoms. The neuropathy in my feet seems better since I started on the B12


I read your previous post, your B12 is dropping. I found this happened when I reduced Levo

Like you, my Levo was dropped from 125 to 100 when T3 was added.

Initially absolutely fantastic, but gradually was less energy

After 2nd blood test (approx 12 weeks on reduced Levo) by then FT4 was bottom of range and I started to get low B12 symptoms back again. FT3 was better than yours, on 20mcg, so no room to increase T3. (Made decision easy)

Increased Levo up to 112mcg , slow improvement in low B12 symptoms. Retested after 8 weeks, FT4 still low, but improving. Increased Levo back to 125mcg. Low B12 symptoms very slowly faded completely. Recent blood test FT4 almost up to level it was before T3 added. now no longer need sublingual B12, just a daily good Vitamin B complex.

Did recently have to reduce T3 from 20mcg to 15mcg, but I think that's more to do with changing brand. I find Morningside stronger than MP

More on my profile

We are all different, but like SeasideSusie, I really felt rubbish when FT4 was lower


I was about to reply to you yesterday evening when I had to go and make dinner as we were going out. Belated thanks for you thoughts. I am ignoring the B12 result from last December as I was taking a multivit containing Biotin which I understand can skew the result. Following most recent result I have started to supplement with 1000 mcg so I'll see where that goes.

I picked up my latest batch of medicines yesterday and was a bit disappointed to see I have been given Mercury Pharma T3 rather than Morningside. I also felt that the Morningside were more effective but had found that my last batch of MP were out of date! I checked that these were in date so will see how I get on. It does make it difficult when different brands seem to have different effects!

Interesting that you also feel better when your FT4 is higher . It encourages me to pursue the line of action.


I absolutely refuse to change brands on T4 or T3

T4 I insist on Mercury Pharma

T3 I insist on Morningside Healthcare.

Mercury Pharma T3 was always just about on its sell by date, also not a blister pack so pills are not as easy to cut towards end of 28 days

Most importantly, I find Morningside is about 25% stronger, than MP at exactly same dose.


I've only been cutting pills since January and sometimes it is more 1/3 ,2/3 rather than halves. I'm just assuming it evens out. I notice the MP T3 have a score on one side - I was hoping that would make the cutting easier. They've put all 84 pills in one bottle - hope they don't get too brittle!


Your t4 will be low because you're taking t3. You look like you need to increase your t3. .


I don't quite understand how taking T3 supresses FT4 if I am also taking Levo. Do I excrete it?


It's because the body only hangs on to what it needs and excrete's the rest.


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