Why are FT4 and FT3 stuck at the bottom of the ... - Thyroid UK

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Why are FT4 and FT3 stuck at the bottom of the range despite increasing Levothryoxine?

London3891 profile image


I'm after some advice please as I can't figure out how to raise my hormone levels.

As I understand it, the aim of levothyroxine treatment is to bring TSH down to the lower part of the reference range which for most people should put their free hormones into the top part of their ranges (and possibly over range). My question is why might that not be happening?

I don’t think my conversion is the issue, as both T4 and T3 are low in their ranges, but it seems impossible to get my levels to rise to decent levels.

Even though my TSH is supposedly in the sweet spot, and I’m taking more levothyroxine than ever (150 5x week, 125 2x week), my T4 was actually higher when I was trialling T3 (no longer taking), and higher when my TSH was 3.7! I know I can continue to increase my dose of levo, but I’m confused that I'm not seeing the correlation I’d expect between a lower TSH and higher hormone levels.

Below are my most recent results:

(All tests taken under the same conditions according to the protocol).

September 2021

TSH 3.69

T3 3.39 (3.1 – 6.8) 8%

T4 13.9 (9 – 22) 38%

November 2021

TSH 0.92 (0.3 – 4.2)

T3 3.6 (2.4 – 6) 33%

T4 11.3 (9 – 23) 16%

December 2021

TSH 0.66 (0.3 – 4.2)

T3 3.2 (2.4 – 6) 22%

T4 13 (9 – 23) 29%

The best levels I ever had were a year ago when my TSH was higher than it is now:

December 2020

TSH 1.34 (0.35 – 4.94)

T3 4.37 (2.63 – 5.7) 57%

T4 16.3 (9 – 22) 56%

(And actually my T3 was 3.6 over a year and a half ago when my TSH was 4.63 before I even started treatment!)

I’m feeling very confused and like it’s not ‘working like it’s meant to’…

Many thanks for your thoughts!

44 Replies
SlowDragon profile image

Do you always get same brand levothyroxine at each prescription

How do you take your levothyroxine

Waking or bedtime

Always on empty stomach and then nothing apart from water for at least an hour after

No other medications or supplements within 2 hours.

Some like iron, magnesium, vitamin D not within 4 hours

Are tests always done as early as possible in morning before eating or drinking anything other than water and last dose levothyroxine 24 hours before test

Approx how much do you weigh in kilo?

Are you lactose intolerant?

Hi SlowDragon, I take liquid thyroxine (always Teva) on waking and have nothing except water for an hour. Then apple cider vinegar with probiotics and zinc, as well as B vitamins and extra folate with breakfast, and then iron, vitamin D and magnesium more than 4 hours later and spaced apart. I weigh 64 kilos. Also take the contraceptive pill (at night) which I think means you need more thyroxine? Not lactose intolerant but diagnosed with SIBO.

greygoose profile image
greygoose in reply to London3891

I think you're probably taking your zinc too close to your levo. Should be at least two hours away.

London3891 profile image
London3891 in reply to greygoose

OK - thanks, greygoose - I'll fix that. Do you think that alone could be why I'm not responding adequately? I would have thought if it was an absorption problem, my TSH would be higher?

greygoose profile image
greygoose in reply to London3891

It probably would, yes. And your pituitary is obviously quite satisfied with your levels - unless, of course, you have a sluggish pituitary. Which is always a possiblity, and one of the reasons why dosing by the TSH is such a bad idea.

Try taking the zinc further away from your levo, for six weeks, and see what your results are on the next test.

But, how do you feel? Maybe you don't need your Frees any higher than that. Unlikely, I know but depends how you feel.

London3891 profile image
London3891 in reply to greygoose

Well moving the zinc would be an easy win so I'll definitely try that. However, I haven't been taking the zinc for very long (maybe 3 months) and I've never had high free hormone levels, and they don't seem to fluctuate much even when the TSH is bobbing up and down.

I posted below to DippyDame about symptoms - essentially I find it hard to know if the symptoms I have are thyroid related or not, but I'd like to know if they'd get better if I could get my levels up. I have been diagnosed with SIBO and I still have digestive troubles (will shortly be embarking on a course of antibiotics and probiotics for that) and I have central sensory hypersensitivity which gives me issues with my nerves, and my mood has also been pretty low for the last couple of months. Perhaps none of these symptoms are related and, as you say, my body might be happy with my thyroid levels where they are...but I'd like to be sure and so raising my levels is necessary in order to find out.

greygoose profile image
greygoose in reply to London3891

OK, I've read your reply to DD, and will say straight away that you do not appear to have a conversion problem. Going by the percentages, your Free levels are pretty close together, which is the way they should be. It's just that both are low. And, judging by your symptoms, are too low for you.

But, you're not on an exceptionally high dose of levo, are you. 150 5x week, 125 2x week Some people just need higher doses than others.

And, I fail to see why, given your levels, you aren't taking 150 mcg every day. What is the point of decreasing it twice a week? Doesn't make sense.

You say that your nutrients are 'good', but what exactly are the results and ranges? Oh, and the B vits should be at least two hours away from levo, too. :)

London3891 profile image
London3891 in reply to greygoose

Thanks, greygoose. The dose isn't exceptionally high, I agree - it's just a lot higher than it was (and it's high if you compare it with the dosing guidelines which suggest I should be on nearer 100 /day). But I'm not averse to increasing the dose, I'm just wondering why so far the increases so far have had the effect of lowering my TSH but haven't pulled up the frees. The reason for the two days at 125 were just the latest incremental increase instructed by my endo (I had been on 5 x 125 and 2 x 150).

Vit D in June was 100 (50-175) and since then I have increased supplements

Ferritin this month was 75 (10-120)

B12 this month was 766 (160 - 800)

Folate last month was 5 (>2.7)

I will move everything away from the levo ☺️... in fact, I'm starting to think it would be much easier to take levo at bedtime and the pill in the morning, but I don't want to have to stop eating 3 hours before bedtime (even though that might be good for me!)

greygoose profile image
greygoose in reply to London3891

The dose isn't exceptionally high, I agree - it's just a lot higher than it was

Well, that isn't really surprising. Our needs change.

(and it's high if you compare it with the dosing guidelines which suggest I should be on nearer 100 /day)

You mean dosing by weight? That is just a suggestion for a starter dose for some people - not everyone could tolerate starting that high - it is not a cast iron rule. We need what we need, not what some medical bureaucrat, who doesn't have a thyroid problem, thinks we ought to need!

I'm just wondering why so far the increases so far have had the effect of lowering my TSH but haven't pulled up the frees.

Yes, I know. But, I'm not sure anyone can answer that question with any certainty. Thyroid - and the human body - is complicated. There are so many variables and not enough research. It's difficult to come up with hard and fast answers to any questions. And, of course, we're all different.

Sounds like your endo is being over cautious. Such a silly little increase! What did he expect that to do?

Your ferritin could be higher. But, have you had your iron tested?

B12 is good, but folate much too low. What are you taking for that?

Only you can decide if you should take levo in the morning or evening. But, two hours after eating should be enough - unless you have a very large evening meal?

London3891 profile image
London3891 in reply to greygoose

Thanks again greygroose! I know it's not possible to answer with certainty, but I always learn something when I post and when I read other threads, so I really appreciate the time everyone takes to engage and offer advice. It's also helpful to get some perspective on what's reasonable or not to ask for in terms of a dose increase - I have an appointment later today and will push for that.

Results from yesterday:

Iron: 24 (9 - 30)

Transferrin 2.6 (1.7 -3.4)

Transferrin saturation 37% (16 - 55)

My ferritin shot up to 100 when I started eating liver, but I was worried about my cholesterol increasing as a result so endo said better to take supplements. I used the oral spray initially but levels fell to 67 in September and my hair started falling out again, so now am taking 20 mg iron biglycinate capsules every day.

Maybe I'll try levo two hours after eating at night - means I'd need to be disciplined and rule out wine / tea / snacks after 9pm! 😏

greygoose profile image
greygoose in reply to London3891

My ferritin shot up to 100 when I started eating liver, but I was worried about my cholesterol increasing as a result

Eating liver isn't going to raise your cholesterol levels. Cholesterol is made in your liver, and your liver keeps it at a constant level. So, the more you eat, the less your liver makes. The less you eat, the more your liver makes.

But what is going to raise your cholesterol is that low FT3. High cholesterol is a hypos symptom.

London3891 profile image
London3891 in reply to greygoose

Hmm, maybe I'll go back to liver then... Do you know if there's a way to raise ferritin without overdoing the iron? I don't actually understand the different elements, but at one stage I got a transferrin saturatin result of 57.95 % (range 20 - 50) and the endo suggested I reduce the iron supplements, so I did, but that caused my ferritin to fall as well.

gabkad profile image
gabkad in reply to London3891

Liver also gives you retinol (real vitamin A) and the B vitamins.

The endo first also tested me for retinol. Seems hypos have low levels of this too but nobody seems to bother testing. It was the first time I'd ever had it tested in my life.

greygoose profile image
greygoose in reply to London3891

Ferritin is a protein that stores iron. The iron blood test measures the amount of iron available to your body. If that level falls, it takes more iron out of the ferritin store. And, when there's extra iron, it should put the iron back into store. But, you're right, sometimes taking iron can over-load the iron in the blood. And, it's said that the best way to avoid that is to eat liver, but I don't know what that's the best way.

The reason you shouldn't eat too much liver in a week, is because it's high in vit A. And, you don't want too much vit A. Not because it raises your cholesterol. :)

Maricopa profile image
Maricopa in reply to London3891

My Moms thyroid med had to be taken alone about one hour before she ate anything. After a few weeks I noticed a big change. We’d have her take it before breakfast in the mornings.

SlowDragon profile image
SlowDragonAdministrator in reply to London3891

You know to stop vitamin B complex a week before tests as biotin can falsely affect test results

I do (but thank you) ☺️

By TSH 'sweet spot" I take it you mean within reference range....not the best way to judge dose requirements but medics are trained to do this which is leaving many thyroid patients struggling!

These papers will explain...



Do you have symptoms of undermedication?

Do you eat soya products? They affect function/ absorption so a No-No for hypos

Have you optimised vit D, vit B12, folate and ferritin....all essential for good thyroid hormone function

Have you had antibodies tested for possible thyroid autoimmune disease/ Hashimoto's....this can cause fluctuations in hormone levels.

There are no rules set in stone for thyroid dosing because that depends on several factors...not just TSH!! There is no "meant to" about it, we are all different with different needs

High TSH = low hormone levels

Low TSH = high hormone levels

Looking at your latest labs...

September 2021

TSH 3.69

T3 3.39 (3.1 – 6.8) 8%

T4 13.9 (9 – 22) 38%

Your results are abysmal, it appears that you have an absorption problem though this was not evident previously....FT4 should be much higher on 150 5x week, 125 2x week.

Under what conditions do you take the levo?

Well away from food and drinks is essential for good absorption

Were the tests done at the earliest appointment in the mornings?

However, your results below were very much better.

December 2020

TSH 1.34 (0.35 – 4.94)

T3 4.37 (2.63 – 5.7) 57%

T4 16.3 (9 – 22) 56%

What dose(s) did you take then?

How did you feel then?

Have you made repeated quick dose changes which have unsettled your hormone levels?

At that point a small increase in levo should have helped....was that tried?

Have you been taking any different medications in the intervening time that may have compromised absorption?

At that point your conversion appears fine..

For good health the active hormone T3 is required by every cell in the body in a constant and adequate supply...your current level of 8% through the ref range red-flags the need for change.

I suggest you start by having nutrients and antibodies tested and by concentrating on the Frees...FT3 in particular. Do not become obsessed by TSH which is a pituitary, not a thyroid, hormone

Just a few thoughts ....



Hi DippyDame, thanks for your reply!

'Sweet spot' was a poor choice of words - I just meant that my TSH is around the level that most sources suggest we should aim for and at that level (according to Dr Toft at least) most people will have nice high hormone levels.

My vitamin B, D and ferritin are all good; folate isn't but I'm working on that. I rarely eat soya and never around the time I take my medication. I follow all the rules around taking the medication and always test at 8am, fasting and 24 hours after last levo dose. I have been tested and have antibodies for Hashimoto's.

I find it hard to know if the symptoms I have are thyroid related or not, but I'd like to know if they'd get better if I coudl get my levels up. I suffered from lots of digestive issues back in December last year, and although these are better, I have been diagnosed with SIBO and I still have trouble. I also have central hypersensitivity which gives me issues with my nerves that all the neurologists I have seen believe was brought on by thyroid hormone imbalance. I take Amitriptyline for this but I the symptoms haven't gone away. My mood has also been pretty low for the last couple of months but then that could be a result of the other symptoms - hard to know!

Last December I had just switched to liquid thyroxine and was taking 100 every day. I did trial T3 for a few months this year but I couldn't get my levels up then and I didn't feel any different so I came off it. I have been messing around with the dose for about 18 months now and my endocrinologist always wants quick blood tests after a change.

I agree with you about focussing on the frees and not obsessing over TSH, and I'm open to continuing to increase my dose. But what I'd really like to understand is why the dose increases aren't seeming to push up the frees.

Could you explain a little more about conversion please? You said it used to be ok...does that mean it isn't now? How do you calculate it?

Thanks again!

DippyDame profile image
DippyDame in reply to London3891

The easiest way to identify poor conversion is by looking at the Frees....high FT4 with low FT3 indicates poor conversion. I cannot see any evidence of that before the Sept labs.

The only thing that comes to mind is that something is preventing the hormone reaching the serum from the gut. The T3 should then reach the nuclei of the cells, via T3 receptors, get to work, and leave you feeling well. You are not getting past stage 1!!

I have a type of thyroid hormone resistance which means it is difficult for T3 to enter the cells....most of it ( basically) just sloshes around the serum doing nothing before being excreted, so my FT3 is elevated. I have to take a huge dose of T3-only. You don't appear to have this problem because FT3 would be high

I said your conversion appeared fine here because the Frees looked that way with T3 at 57%. How much T4/T3 were you taking then. The amount of T3 may have made considerable difference. Were you still taking T3 at the time of the Nov results?

TSH 1.34 (0.35 – 4.94

T3 4.37 (2.63 – 5.7) 57%

T4 16.3 (9 – 22) 56%

The T4 that the thyroid produces is the storage hormone, to become active it has to be converted by the removal of one iodine atom (in various tissues in the body) into the active hormone T3 .....that is 4 atoms reduced to 3, hence T4 and T3.

However it looks as if Hashi flares might be at least partly responsible for your fluctuating levels

Have you tried a gluten free diet.....this helps many with Hashi's.

I'm not sure than this may be the answer you need but look into anything that you might be taking med or food wise that may be affecting absorption into the serum..

This might get you started


"Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function?"

Please let us know how you get on.

London3891 profile image
London3891 in reply to DippyDame

Ok, thank you. Good to know I don't have a conversion issue. I have previously tried going GF a couple of times but it never made any difference...

DippyDame profile image
DippyDame in reply to London3891

Sorry I hit "reply" by mistake....I've now added more to that reply!!!

London3891 profile image
London3891 in reply to DippyDame

Thanks for the rest of the post too! I'm curious about whether if I can treat my SIBO that will improve things. I do think if it was an absorption issue though, my TSH would probably be higher?

I only took T3 from April to September and none of the results I posted were when I was taking it. The results I posted with the higher FT4/FT3 were from when I first started taking liquid thyroxine and was on 100 / day.

DippyDame profile image
DippyDame in reply to London3891

Addressing SIBO may very well help.In many patients with SIBO, reducing inflammation and eating a nutrient-dense diet can help restore thyroid function ...and gut function

I mentioned possible interactions with drugs you may be taking which could affect absorption. You could try checking these on DrugBank, enter the name of the drug in the appropriate box down the page and enter. I've opened the Levothyroxine page at the top.


However, if the hormone isn't reaching the serum from the gut (due to poor gut to serum absorption) then it will not affect TSH to any great extent.

The pituitary will not then be able to detect a raised hormone level in the serum (that hasn't happened due to low absorption !) which would instigate a change in TSH level, and consequently the amount of hormone produced by the thyroid gland .... despite swallowing a reasonable dose of hormone.

So an absorption issue may very well be affecting TSH.

It could be that when lab levels were higher it was because the liquid levo was being absorbed into the serum more effectively than the tablet form.

Unfortunately there are many variables that can get in a tangle and sometimes they just need to be slowly unravelled!

Good luck!!

London3891 profile image
London3891 in reply to DippyDame

Thank you, DippyDame 🙂

DippyDame profile image
DippyDame in reply to London3891

Finally... and I know I've said more than enough already!

I suspect you are overthinking this problem and grasping at anything that you think might help, without taking time to look closely at what you really need to do. Easy when you are struggling!

With the info you have been given, list your options, work out a plan to change the way you medicate then stick to it for 6/8 weeks....anything less is pointless! One slow step a a time.

Your dose changes and testing have been too fast/ soon....you are confusing your body.

Only you can decide what you should do, nobody is going to give you a detailed route map because we don't experience your individual collection of issues. We can only share our own experiences and what we have learned.

I'm clearly not a medic, just an ancient patient who has had a very long bumpy, convoluted, journey passing through some very dark places before finding the way forward, so I empathise with anyone struggling to feel well...it's hard work!!

Hope you feel better soon.

London3891 profile image
London3891 in reply to DippyDame

Thanks for the lovely message and wise advice, DippyDame - I'm going to do exactly as you suggest 🙂

wellness1 profile image
wellness1 in reply to London3891

Have any of the neurologists explained why they think your central hypersensitivity was brought on by thyroid hormone balance? Have they given you any information to explain this? Is this a sensitisation that results in pain? I'm sorry to hear the amitriptyline isn't helping with your symptoms and I hope you're being offered some other support.

London3891 profile image
London3891 in reply to wellness1

Hi wellness1, thanks for your message.

They all say that this sort of central sensitivity can be caused by some sort of imbalance or event (could be stress, trauma, menopause etc.) and in my case the only thing that it seems to coincide with was untreated hypothyroidism. It's something that some people are predisposed to apprarently (oddly one neurologist said everyone who is hypermobile has it) but I think they expected the symptoms could be 'shut down' with neuro-regulators (like Amitriptyline). The sensations only cause mild pain, and t's very fleeting, so not something that would be worth worrying about from a discomfort perspective. It's more a reminder that something's not right and I'm currently stuck on drugs that I'd rather not be taking and wondering if the random sensations will ever go away... GP wants me to read about thinking differently about pain and join a support group, but I want to try to get to the bottom of the physiological cause and deal with that.

wellness1 profile image
wellness1 in reply to London3891

It sounds like the mild fleeting pain is more like neuropathy, rather than a chronic pain condition. I'm learning about sensitisation in the context of persistent pain but it sounds like you're referring to something else. Thyroid hormones definitely have far-ranging effects but I wasn't sure how it would apply to sensitisation. If that's what the consultants think caused this, it must make not getting your thyroid situation sorted all the more frustrating. I hope you're able to make some progress on that front and it brings relief. Good luck with your digestive issues, too. I often think so many things are interrelated or that one thing can affect another but medical care is very specialised.

London3891 profile image
London3891 in reply to wellness1

Totally agree - the interrelationship thing is far-reaching and overwhelming sometimes. The central sensitivity I have is part of the umbrella of chronic pain conditions (like Fibromyalgia, IBS, tinitus etc.) - there's no neuropathy or physical component, it's about how my brain percieves sensory signals... and it seems to have got a bit destabilised and miswired. Thanks for your messages and I hope you too get some resolution on your persistent pain... it's disheartening when things go on and on isn't it! Fingers crossed for both of us 🙂

When you say your endo likes quick blood tests after a change. ...how quick ?hopefully 6 weeks at the very least .... i think sometimes our TSH can lag behind changes by a very long way.

On the "it doesn't make sense" front .... Just for comparison.. i needed 150mcg for over a decade despite my dose/ weight estimate being about 96mcg... i now seem to need less ,but still need 112.5mcg.

So ignore the 1.6mcg /Kg it's just a statistic.

Also regarding the TSH... mine ended up at 0.05 -0.1 ish, and pretty much stayed there, and i was relatively well with that , even though my fT4 wandered around from 60% to 120 % for no apparent reason.

I now think after seeing many many results histories on here, it is not at all unusual for the numbers to 'not do what they are supposed to do' . Mine certainly don't.

I got TSH 2.9 /2.5 /2.7 on Levo 50 /100/150mcg. after i'd been on each dose for months

Then a year later ,still on 150mcg , TSH went to 0.05-0.5 area and stayed there.

More recently I've had fT4 going up loads when i reduced dose slightly, and going down loads when i increased slightly , and i was scrupulous about test conditions being consistent.

So i say ~sod the numbers (for now ) .... use simple logic .. you know your T4 /3 are pretty low....so if you want to know what higher fT4/3 feels like, increase the dose to 150/day and see how it 'feels' for a few months.

Good advice, thank you tattybogle! Your results sound even less understandable. I think you're right (like greygoose says too) that there's no harm in increasing and seeing whether I can get my levels up and how that feels

Also, I always have to get blood tests less than 4 weeks after a dose change so agree with you body is probably not getting the time it needs to adjust before I make the next change. I've had over 15 endocrinology appointments in the last 18 months and I reckon I've probably changed my dose 10+ times...

i strongly feel the body is striving for stability..it is very busy compensating for everything that changes ,and i suspect if only finds time to improve random symptoms when it senses that stability has arrived and is reassured that everything isn't going to be changing again shortly. The whole complex HPT axis seems to have evolved to keep fT3 at stable levels despite whatever else is going on / or put into it .. it adjusts TSH and fT4/3 and conversion to T3/ or reverse T3 to do this ... i reckon 4 weeks after a dose change it's only just figured out what the new level of fT4 actually is .. and is probably only just beginning to decide what to do about it at that point.

Last time i made a very small adjustment to Levo dose .. i was only able to say it was an improvement in how i felt after about 4/5 months on it , but i'm now very glad i didn't just change it back again after 2/3 months .... if i'd gone by how i felt for the first 5/6 weeks , i would have changed it again.. and i daresay knowing my blood results wouldn't have been much help at that point either.

I reckon your body's response to 10+ dose changes in 18 months is probably "WTF is going on ? "

If i was in your position i'd go up to 150mcg and not think about it again until spring. (and that's much cheaper advice than an endo will give you :) )

😂 I think you might be right - it does all sound a bit nuts when I read back my posts! Thank you and fingers crossed.


When you had the good results, both FT3 and FT4 over 50% in range, were you taking less Levo than you are now?

If so, then perhaps, like me, you might have an issue whereby your body is producing too much Dio3 enzyme and converting the T4 into reverse T3 and expelling it. So it's doing nothing for you. I'm only just trying to get to grips with this myself. I take a combo of Levo and T3 and it hasn't been helping (as you say your T3 trial didn't). So having read Paul Robinson's book Recovering with T3, I am currently experimenting with reducing my Levo dose. It might not be a case of "more" for you. It might need a different balance. Less Levo and more T3. I went from 125 Levo to 100 and increased my T3 by 5mcg to 40mcg a day and for the first time in several years I was able to walk properly. A proper gait and speed. That's wearing off again now, my body has caught on perhaps and is busying itself producing more Dio3 to convert the T4 to rT3. So I'm going to try reducing to 75mcg Levo a day and see if I get that improvement again.

I have never felt any better on Levo. In fact I have felt much worse than when I was diagnosed and treatment started. The move from 50mcg of levo a day to 75 was brutal. A few years ago, when I was on 100 Levo a day, I found that if I felt particularly bad I could skip a day's tablets and feel wonderful for that day. Energy, ability to walk and do things. The following day if I didn't take it again would not be so good. The day after that much worse and then by about 5 days I'd cave in and take the Levo again. I didn't have T3 to experiment with then.

Anyway, it's a thought. I'm not far enough down the route to be able to say for sure if it will eventually work and the T3 will help me. But our test results over time have been quite similar. Mine are all up on my profile if you want a look.

Just looked at your results - sounds like you've had a terrible time of it, FancyPants54. Sorry to read about it and I hope you get somewhere much better with T3!

I hadn't actually considered reverse T3 as I thought that would show up as a problem converting T4 into T3, whereas both of my levels are low. I can ask my endocrinologist about this though. Did you have Rt3 tested?

No I haven't tested for it. But my endo did suggest we might do that in spring after I've got my Levo dose down and stabilised and T3 up a bit. It's guesswork to some extent. But the way my body refuses to gain benefit from T3 and the way my blood levels look despite never missing a day's medication unless I do it on purpose, leads me to think something is going on that we can't easily see and so we need to try and see how I feel on less Levo.

It will be interesting to hear what you learn. In the meantime, lots of luck with your mission!!

June25 profile image
June25 in reply to London3891

Reverse T3 is a symptom, not the problem. The issue is that D3 enzmes have upregulated (increased) probably because your body is reacting to what it considers a thyroid hormone overdose. They are getting rid of excessT4 by turning it into Rt3, This alone will cause a drop in FT3 (less FT4 to be converted) but D3 enzymes can also convert T3 into inactive T2, so both of these things can be going on.

You can read about thyroid hormone metabolism here:


I agree with FancyPants54. Your body has decided it has too much thyroid hormone and it is dumping it, both T4 and T3 via the D3 enzyme mechanism. No point continuing with this strategy of more and more levo. Your figures are telling you it's not working.

Some people have a lower set point than average. The setpoint is the ratio between TSH, FT4 and FT3. For them, to increase FT3 they need to reduce their T4 dose and increase their dose of T3. Some have to eliminate T4 completely before their FT3 becomes optimal and they feel well.

London3891 profile image
London3891 in reply to June25

Hi June25, thanks very much for the information and the link to the SPINA test. I have to confess, I find it pretty technical and difficult to follow but good to know that this exists. I wonder if my endocrinologist would be supportive and help interpret the results - I might try next time.

I think I'm going to give it another 6 weeks on levo only and see if things settle, but then may have to explore T3 (again) as you suggest. Thanks again :)

I suggest you run the SPINA test on your results from T4 monotherapy. This test may give you further insight as to what is going on.

Here's how to do it:


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