Thyroid UK
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Can you take too much T4?

Hi All

I was wondering if anyone feels the same as me or has any ideas :-

I am taking 150mcg Levothyroxine (recently increased from 125mcg) & still have all the horrid symptoms of hypothyroidism (or could it be my fibromyalgia?) sore aching muscles -breathlessness, dry skin /eyes, extreme tiredness, throbbing sensations in legs feet / etc., etc., especially after sleeping when I feel these symptoms are much worse! When in my mind they should be eased after resting?!!!

So could it be that as I'm taking my T4 regularly every morning that it is overloaded in my system & not converting to the active T3?

So therefore keeping me in the hypo stage ?

Or could it be that I am having a fibromyalgia flare? ((These two seem to be so inter-related)

My question being:- If I stopped T4 for a few days - (to balance it out) would things improve? - Can you overload on T4 ?

Incidentally I have tried T3 (& reducing T4) advised by my endocrinologist- but then went hyper with racing heart/palpitations etc., so was told to stop T3 & because of this he felt I wouldn't tolerate NDT!

Now I don't know where to turn as he has referred me back to my GP who says all my tests are normal - you know the rest - --------- Keep taking the pills !!!!!?

I hope this makes sense to anyone out there !!!

I'm really fed up of going to bed/resting thinking I'll feel better when I wake only to actually feel 10 times worse !!!!

But then again if I don't stop & rest - I am equally good for nothing ?!!!!

Doesn't seem to me to be an answer to all this at the moment.

Any response would be greatly appreciated- So thank you in advance.

26 Replies

Sutton, you can, which is the reason thyroid bloods are tested, to see that you are neither over nor undermedicated. If you post your recent thyroid blood results with the lab ref ranges (the figures in brackets after your results) members will advise whether you are optimally medicated.

Low FT3 is often the reason hypo symptoms are experienced and increasing T4 doesn't resolve it if you aren't converting well. Were your FT4 and FT3 over range or were you just experiencing symptoms of racing heart and palpitations? It might have been better to reduce your T3 to see if you tolerated the lower dose. Some people don't tolerate synthetic T4 &/or T3 but they do very well on NDT.

Ask your GP to test ferritin, vitamin D, B12 and folate as hypothyroid patients are often deficient/low and these deficiencies can cause musculoskeletal pain, fatigue and low mood similar to hypothyroid symptoms. Post your results with the lab ref ranges (the figures in brackets after your results) in a new question and members will advise whether supplementation is required.

I was over-replaced on T4 to suppress TSH but halving dose over 7 months didn't improve breathlessness, tremors, parasthesia, debilitating palpitations, diarrhoea and weightloss or pain. Endo thought I had fibro and COPD. They all cleared 12 weeks after I stopped T4 and a lung function test found no sign of COPD. I was able to reintroduce T4 but can only tolerate it with T3 which seems to calm things down.

1 like

Thank you Clutter

I am waiting for a copy of recent blood tests which I will post ASAP. I do take 1600iu Vit D daily & have sleep apnea diagnosed 6 months ago (for which I use a CPAP Machine at night). I also started having sleep seizures 15 months ago (6 so far). The medics are not sure whether these are linked to sleep apnea or are epilepsy - I am not taking any medications for seizures at the moment as I couldnt tolerate them.

I'm thinking that could be linked to the thyroid !!!

Anyway can you suggest how much T4 & T3 I could start with to see what suits me - I'm on 150mcg T4 (which was only recently increased from 125mcg) - I have a few 20mcg T3 left - I'm not really sure where to start .

Many thanks


Sutton, try 5mcg T3 daily to see how you tolerate it. It would be easier to advise if I could see your recent thyroid bloods.


I was on 100mcg T4 originally. - he reduced to 75mcg T4 & 10mcg T3

I'm now on 150mcg T4 (recently increased by GP from 125mcg )


It is possible that your medication is being inhibited from absorption from other hormones/medication. You mentioned that you have high cortisol levels, cortisol is a major absorption inhibitor of t4 and t3. But t4 is also inhibited by food intake, calcium carbonate, antacids, easteogens and many others. Many people seem to take their t3/t4 at meal times and don't realise that taking it with food will seriously inhibit it's absorption. Thyroid hormones should be taken 1 hour before food, or 3 to 4 hours after food. This is because the hormone is easily absorbed into the system with the stomach acid from fasting. I hope this is helpful. Even my ENT specialist didn't know about this research, even though much was researched from published medical research material and often on the endocrinologist society website.


Thank you, I have just learnt something, amazing the amount of info this site contains which is helpful


Soya also inhibits uptake/conversion of hormones. Fermented soya is apparently ok though.




Hi Sutton210, I have had very similar symptoms to you. I reduced my Levo and actually felt better for a short time (was experiencing palpitations/anxiety) but then my THS shot through the roof. Started t3 only but ended up in hospital because my heart went crazy. Long story short, I'm now on beta blockers for my heart and a combo of Levo & t3, starting on a low dose & building up gradually. Even though I'm not out the woods (TSH 8.3 t3 3.3) I'm feeling better now than the whole time I was on Levo only even though my TSH was much lower then.

Keep going back to the drs and try different combinations of t4 & t 3. I'm also gluten/cafene free and take vit supplements. There is something that will work for you.


Hello Isis64

Thank you for this reply. I do have a small supply of T3 left that the Endo gave me - can you suggest how much I could try reducing my T4 (150mcg at the moment) & how much T3 (20mcg pills) I should introduce please .

When I was on 100 T4 he reduced to 75mcg & added 10mcg T3 last yr - at that time I didn't know much about altering the doses myself -as you always think the doctors know best !! I know different now!!


If 75 mcg T4 plus 10 mcg T3 made you hyper, then try 75 mcg T4 plus 5 mcg T3. Break the T3 tabs into quarters. (If I read correctly what you wrote.)

Or 100 mcg T4 plus 5 mcg T3.


I'm sorry I really don't know enough to advise on dosage for other people, especially as I'm not sorted myself yet. I just wanted you to know you are not on your own. I think a lot of people struggle with the meds that we so desperately need. I'm lucky enough to have a Dr who is willing to work with me to find a solution. For me, it's a combination of t3, t4, beta blockers, diet and supplements.

I know how frustrated and worried you must be feeling. I thought a tablet would make me feel better and I ended up getting worse! Get your latest test results & post them here and make sure you're tested for the things mentioned by reallyfedup. Clever people will be able to advise you. Do what you can to take control of your health. Be patient and don't ever give up. Like Chloe said, we will get sorted yet!


If you're taking Beta-blockers you should keep an eye on your B12 and magnesium levels, because they will probably go down.

Beta-blockers are actually not recommended for hypos. Why are you taking them?


Hi Greygoose, i've had palpitations ever since I started taking thyroid meds. They got so bad I stopped taking Levo, but TSH shot up to 18.3. Started low dose of t3 but ended up in hospital when my heartbeat wouldn't slow down. Saw an endo in hospital who put me on a low dose of beta blockers. My doctor hopes once I get my thyroid meds sorted, I can come off the beta blockers, but I still have mild palpitations on them. I'm going to wear a heart monitor for 24 hours as drs aren't sure if my heart problems are caused by thyroid meds or are completely separate. B12 853 so ok at the moment. Thanks for the heads up.


:) How's your magnesium? Low magnesium can cause palps, too.


Yes, you can certainly over dose on it. You need TSH, T4 and Free T3 to check, only way.Hypo and Hyper can cause the same symptoms, mine do, endo said so.



I'm in exactly the same position and have stopped levo - fast pulse slowed to normal and palpitations gone but have been told by gp there is no other treatment other than go back on T4!!! Thanks to this forum I was able to say there are other options so I'm waiting now to see what will happen after gp speaks to endo. In the meantime I am struggling with hypo symptoms like yours.

Keep battling - you're not on your own - we will get sorted yet! Let me know how you get on.


Thank you for this - I will let you know how I get on - please also let me know how your doing - we can compare ! How long have you stopped your T4 & how much were you on?


Without knowing all your test results especially b12 and ferritin and folate its impossible to comment


I was experiencing the exact same symptoms you describe even while on my Thyroid meds.

What actually helped more than anything was eliminating ALL (and I mean ALL) processed sugar from my diet. I could tell the difference within 48 hours.


Good answers all around. Some people do not do well on T4. It can turn into reverse T3 which is not good and blocks T3 causing major hypo symptoms. So, you can be taking too much T4 or you can be taking the right amount of T4 but it is not converting into T3. It takes investigation. There is a lot to learn.

Sometimes T4 just doesn't work for some people.


Sorry, but I cannot understand your statement "100 synthroid with 25 cytomel is equivalent to 120 synthroid." Afraid I don't follow that.



Trend, T3 is 3 x stronger than T4 so 100mcg T4 + 25mcg T3 is equivalent to 175mcg T4.


Trend, that's probably because of the T3 in NT. I was very ill on T4 only but I'm fine on T4+T3.


Trend, NHS doesn't even test rT3 as far as I know. I was vitD deficient last year but they don't follow up once the deficiency has been corrected. Endo has requested a vitD test in Dec but I think it's because I've recently been diagnosed with mild osteopenia.


Trend, 75mcg T4 + 30mcg T3.


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