Thyroid UK
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T4 headache!!!

Hi I currently take 125mcg of thyroxine per day but a few hours after I take it I get a very bad headache at the front of my head and sometimes behind my eyes. It feels as though my brain is bashing against the front of my skull. I'm not prone to headaches but it always seems to be after I take thyroxine. Also I came over a little heady/dizzy.

Is it possibly a T3 conversion issue or am I not giving enough time for the new increased dosage to work? I've been into my increased dose for 3 weeks now.

Any advice would be greatly appreciated.

Thanks xx

17 Replies

This is difficult to know. It sounds like it could be that you are taking too much. It could also be, like you say, a conversion issue but as t4 is such a long acting hormone I would be surprised. Of course we are all different so I could be wrong :)

Did the headaches start after your increase? I think you need to discuss this with your doctor and see what the result of your next blood test is.

You also need to make sure your iron and ferritin levels are good.

Carolyn x


Hi Carolyn thanks for your reply.

Not sure about whether it's too much I'm taking or not. It has been since the increased dose but I'm wondering if it was too much of a jump from 75mcg straight onto 125mcg. Also it happened within the space of an hour or two and my head felt very fuzzy. The headache got so bad that in the end I went to bed and slept for half a hour. I woke up and felt a lot better.

Iron level from August was 15 with normal range at 30.


Jo xx


Your iron level may be the problem if it is low. You may not be able to tolerate such a large increase. You may find you are better on 100mcg for now until you can get your iron level up to normal. If you take iron, make sure you don't take it within 4 hours of your thyroxine. You may find that once you get your iron level up a bit you can tolerate the thyroxine better.


Hi Carolyn thanks for your answer.

Apologies for my brain fog, I actually experienced the headaches even before that increased dose. They started around about when I was told to increase to 75mcg but were much worse than they are now which is odd. Could it be that I'm generally just tired?

If it's possible I'm on too much thyroxine too soon instead does that mean I'm now going into a hyperthyroid state? I didn't think such a reaction to the thyroxine would've happened so soon. The GP said for me to return sometime in October for a follow-up but if I'm experiencing problems now should I be seeking help from them sooner?

Due to the fact I'm on meds treating the hypoT, I'm concerned about losing weight through the thyroxine. (as hypoT patients are classically overweight but I'm not so can't identify myself as being hypoT at all) I'm just an ounce under 8 stone, BMI 19.5 (normal), and I've been working hard to keep as much weight on as I can as at the start of the year I weighed 7 stone 3oz, BMI 17.9 (underweight). I really don't want to go down the route of losing any weight again. :(

Thanks x


Do you have your most recent blood test results? That could help to clear things up.

Other things could be causing the headaches with the thyroxine, such as low iron. This really does need to be addressed. Low iron can cause symptoms even when people are not on a high enough dose to be hyper. It's not the same as being hyper, just some of the same symptoms.

Not all people who are hypothyroid are overweight, although most are. Some people find they struggle to eat when they become hypothyroid and this can result in weight loss. Just make sure you are eating plenty of proper foods. Protein is important so that you don't lose lean muscle mass.

It might not be that you are on too much, just that the increase was too quick for you given your low iron. I'm not a doctor though and we are all so different. It is just a suggestion of what might be the problem. Perhaps discuss with your doctor if these headaches don't ease up :)


Hi Carolyn, thanks for your reply.

The only blood test I have is that for the TSH which was tested after I was put on thyroxine initially. That came back at 4 (normal range 0.2 - 4.2) Doctor seemed quite pleased at first but he completely forgot I was on thyroxine and when I did explain to him that I was he came over more concerned or should I say maybe slightly unhappy with the result.

I took 100mcg instead of 125mcg today to see if that would make a difference and I did have another headache today but I guess it will be a few days before any improvement. If the headaches are still recurring after each dose I'll be going back to my doctor but I'm just worried that I seem to be the only patient they see with such problems. :(

Jo x


Sorry, I can't quite remember, but do you have low iron? If you do, it is important to get it treated. That could be causing your symptoms on thyroxine. Iron is important for conversion and many other things so it is important to make sure this level is good. Ferritin seems best around 70-90 for most people.

If you don't feel any better on 100mcg after a few days, perhaps it is something else, in which case maybe go back up to the 125mcg your doctor suggested. It's just that some people find increases difficult and find it easier to do it in 25mcg increases. Some people have to do it more slowly than that.

Folate and vitamin B12 are also very important, particularly the latter.

I hope you find the answer.


Hi Carolyn, yes I do have low iron. I currently take iron tablets for it.

I took 100mcg yesterday and today and the headaches are still there, so I'll just see what happens for the next few days.

Maybe I should also get tested for folate and Vit B12 deficiencies, although I don't know if these are things NHS doctors typically test.



It would be a good idea to ask about these, especially as your iron is low. They work together with iron to make healthy red blood cells, among other things.

Deficiencies in any of these could be causing you to get headaches from your thyroxine. They are important for your body to properly convert and use thyroxine. It could be that your body isn't able to do this very well at the moment because of your iron deficiency so it is important to get your iron level up.

Carolyn x


Yes could be you have increased too high too quick. Usually they increase by 25mgs until right dose. I did have headache when I first started on even 25mgs but took paracetamol and a few days later it subsided. It happened each time I increased but subsided in a couple of days. Obviously if it had gone on and on I would have told doctor. Your body has to adjust each time.


I find I get a headache even on 25mcg of levo. It does not go away with time or increase of dose. Am currently on NDT at moment. Not well yet but no headaches.


Hi Lizzie, thanks for your reply.

I have to admit, the first day I took 25mcg of Levo (on my starting dose) I had a horrible attack of diarrhoea. Only one day of it and then it was gone. Strange.

I'm thinking of going on NDT but I've heard that it's hard to get a GP to put people onto it. This is all so confusing for me.

Thanks and hope you get better soon.

Jo xx


Jo- Whether the Levo is a direct cause of your stomach upset is hard to tell on one event.

I had a week of stomach gripes on 12mcg [ 1/2 dose ] Levo on starting, due to initial BP surge. After getting to full 25 dose the stomach was OK, though other effects like fuzzy brain went on for weeks.

Three things here,

1- that Levo is a long acting hormone [will need time to settle] and

2- that side effects can be spurious and last for a day or weeks and

3- your weight is half mine so you're bound to notice a dose 4x my startup dose -on half my bodyweight on TOP of 6x standing dose.

That's 10x [pro rata] daily, what gave me the gripes for a week!

Drs underestimate side effects [they get inured to them in others ;) ] - nor can they stop and stare at every blip on the chart or they would pack their job in!

I think Dr was remiss in missing your taking Levo and overdid it when realising- as your TSH was way too high for being treated with Levo for some time.

If your headaches persist then stress this fact to GP but with this illness it's a long , often uncomfortable, haul.

Consider,also, that early migraine type symptoms may be being triggered. Watch out for visual aura or numbness in face.

It can onset with stress coming down, strangely.


Hi Tegz thanks for your answer.

Yes, I figured that my TSH was still too high due to the look the doctor gave me and also because I read on a website that the therapeutic dose for TSH for someone on levo should be at least 3. Is that correct?

Also he's determined for the TSH to be at least 1 when I next go for a blood test but my illness is just so changeable I don't know if that's going to work.




Yes, it is common for most people to need a TSH below 1 and this is a very sensible place for your GP to aim for. You might be finding it difficult to get there because of your low iron. It makes it very difficult for your body to convert the thyroxine and to use it in the cells and I expect that is contributing to your 'thyroxine headaches'. I think you will find it easier once your iron is up, but this might take a while. Take your iron with vitamin C and make sure you are taking a b vitamin complex that contains vitamin B2 to help with storage of the iron.


Yeah, body language is telling :)

On that point, go on how you feel, not numbers, as the Docs are prone to do.

The lowest TSH in healthy people in a recent report I copied gave 1.4 as the sample minimum with a 2.4 max.

This tallys with the US lower figure of 3 being a working limit for UAT.

Figures on this site have given quite low figures as acceptable, but there's no target - just how you feel .

The lower you go the greater the risk of hyper kicking in!

My labs quote 0.27 TSH as minimum 'normal'.

My recent test came out at 1.5 on 25mcg Levo and I do feel stable, if not great, at that.

I'm hoping to get below 1.0 without having any palps etc. but have to watch this for various reasons.

Sounds like you may be the same- but in greater need of getting there!


I had a total thyroidectomy 2 years ago and after was put on just T3 - felt better than I had for years, after 16 months I was put back on Levothyroxine, 150mcg and started to get headaches also hands and feet hurt, pain in left side in bed enough to keep me awake. I asked to go back onto T3 but had to settle for a mixture of both, 20mcg T3 and 125mcg T4 the headaches are the worst but all the other stuff too, so I started to reduce T4 and take a bit more T3 but even on 50mcg T4 still getting headaches, I see the surgeon next week and the oncologist in January so I hope they will try to sort me out, I have got to the point of not taking Levothyroxine at all, but dont have enough T3 to do that, my original dose was 3 x 20mcg 3 times a day.


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