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Thyroid UK
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Is Levothyroxine causing severe muscle cramping and brain fog?

I had thyroid cancer about 34 years and had my entire thyroid removed and was on Tertroxine then changed to Thyroxine, currently 125mcg daily. For years I've had muscle issues, mostly cramping but getting progressively worse. I even had to stop a yoga class due to cramping and muscle spasms during the class. I'm 58 though look much younger but feel like an old lady with aches and stiffness. I also feel my memory is terrible and worry I'm getting early dementia. These issues have prompted me to see my GP next week as after doing some thinking and researching I feel Levothyroxine may be the common denominator and I've read some of the posts here which convinces me more. People complain of muscle pain and stiffness but I get frequent and excruciating cramps then tenderness and tightness/stiffness which started in my legs but now affecting other parts of my body. There are other lesser problems which may or may not be connected. Fingers crossed I can get this sorted out. I've been worrying what is causing this thinking I've got some muscle wasting disease but think I'm on the right track. My GP is pretty good so think she will be supportive. I'm going to keep reading through the posts here and any responses will be appreciated.

26 Replies

There are various common causes of cramps that afflict people with or without thyroid problems.

Low iron is one, as is low magnesium, and low potassium. There are probably a few others, but I can't remember them off the top of my head.

People with hypothyroidism tend to have low stomach acid, which means that they end up short of all sorts of nutrients because their gut doesn't break down their food well enough.

Having low thyroid levels won't help for all sorts of reasons.

If you haven't had full thyroid testing recently ask your doctor to do the following tests :


Free T4

Free T3

Thyroid antibodies

Vitamin B12

Vitamin D


Ferritin/iron or (preferably) an iron panel

Full Blood Count.

Once you've had the tests done make sure you ask for a copy of the results including reference ranges, copy them into a new post on here and ask for feedback. If you live in the UK you are legally entitled to get given copies of your blood test results. I'm not sure what you are entitled to elsewhere.

There is little point in testing magnesium levels. The test is not very accurate. As long as your kidneys are functioning reasonably well you can just go ahead and supplement magnesium.

Magnesium comes in many forms for supplementing. Choose the one that appeals to you the most from these lists :




Personally, I take magnesium citrate at a dose of approx 300mg per day. It has a slight laxative effect which I find helpful (but some people hate). It also makes me feel slightly sleepy so I take it just before bed.

Potassium is best increased by eating potassium-rich foods rather than supplementing.


First thing is do you have any actual blood test results? If not you need to get hold of them. You are entitled under data protection laws.

You may be able to view test results online - ring and ask about this. If you can then apply for online access to your account. All GP practices are supposed to offer this, in reality very few have blood test results available online.

If not then ask for print out of recent tests. Pick up in a day or two. They may make a nominal charge for paper.

You need to know results for TSH, FT4 and FT3.

Essential to test vitamin D, folate, ferritin and B12. Always get actual results and ranges. Post results when you have them, members can advise

Dr Toft, past president of the British Thyroid Association and leading endocrinologist, states in Pulse Magazine,

"The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l.

Most patients will feel well in that circumstance. But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

You can obtain a copy of the articles from Thyroid UK email print it and highlight question 6 to show your doctor

please email Dionne:

Prof Toft - article just published now saying T3 is likely essential for many especially if have had thyroidectomy or RAI


See if you can get full thyroid and vitamin testing from GP. Unlikely to get FT3

Private tests are available


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results


Love it!


Thanks for the info. I'll be following the advice when I go for the blood test.


I suffered with muscle pain, cramps, stiffness and fluid retention, fluid in knees from levothyroxine - yes.

Levothyroxine also made my sweat smell like sour milk.

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You may not be on enough medication. DO you have reuslts for TSH, free T4, free T3, TPO and TG antibodies, ferritin, folate, B12 and vit D. Less than optimal B12 and vit D can cause brain/neurological symptoms, and aches and pains, as can insufficient medication.

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Those would be my first thoughts too.


I will be going to my GP next week to ask for full blood tests. Are the results always conclusive though? I've decided to stop my meds for a few days so when I see the doc I can say whether there's been any improvement...hence the symptoms may be down to Levothyroxine not being tolerated? This is Day 3 and I think the muscle cramping and spasms are improving.


If you stop your meds for more than 24 hours, the blood tests won't show whether you were on enough medication or not and (if you tell him) the GP will probably ignore them and assume that the dose was OK and that you are a non-complaint patient who should not be taken seriously. Stopping meds for a few days often makes you feel slightly better as your pituitary flogs your thyroid again and so it may produce more T3. However it is harmful in the long run and causes your whole system a lot of stress. A better way to find out if it is the fillers in the tablets causing problems is to take an antihistamine tablet about an hour before the levo.


I've had a total thyroidectomy! I only get Thyroxine from the tablets.


In that case, do not stop taking meds or you could die! Your TSH might still rise for a few days (as your pituitary doesn't know your thyroid isn't there any more) and improve T4 to T3 conversion (doesn't happen in the thyroid) while there is still some T4 left. Luckily T4 has quite along half life.


Thanks for the advice. I usually take antihistamines about every 2 days for allergies.


Stopping tablets is very definitely NOT a good idea

For a start any blood tests are useless. You must only test after minimum of 6 weeks on exactly same dose everyday. Only delaying the dose in twenty four hours prior to test

Yes you feel better initially, when you stop taking Levothyroxine, (it's a well recognised phenomenon ) but you soon feel a whole lot worse.

You will now have to wait 6 weeks after you restart taking daily dose, otherwise test will be pretty useless. All it will show is you have not been taking medication

GP extremely unlikely to test FT3, may not even agree to run anything more than TSH

If you can get vitamins tested that would be better than nothing


I'm no expert Eudora but stopping g your replacement will only confuse things. You need to know your levels as stated against your current dosage and concomitant symptoms. Then you can work out whether you are too high, or low or not converting the levo into t3 efficiently. Your labs will be inconclusive until you get back on your dose, and work it out from there. Post your labs here, the support is fantastic.

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Thanks. I'm only withholding meds for 4-5 days to see if the symptoms improve (Or even worsen). I won't be doing the blood tests until at least several days after I'm back on meds. I need some proof whether the Levo is the direct cause of the muscle problems regardless of blood tests which I have done on a yearly basis anyway and always told are within normal levels. I will be posting results here for feedback. I'm in the UK and unsure whether the tests we can get on the NHS are as detailed as what it's advised here to do.


It's rare for a gp to request more than TSH, but you say yours is supportive so he may do more.

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My side effects whilst taking Levothyroxine (6 years on this medication) Diagnosed with Fibromyalgia, extreme fatigue, brain fog, headaches, sweating, weight gain, hair loss, irritability, breathlessness, sleep apnea, in short my life was destroyed and I was forced to end my career. I managed to get a Doctor to prescribe WP Thyroid and am now healthy and feel as though I have a new life. Keep trying with different meds to see what suits you! And be persistent until you feel better because NDT meds ARE available on the NHS...do not be told otherwise!

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Thank you. I'm so glad I found this site. The responses have been informative, reassuring and encouraging. I've also suffered some of your sumptoms as well as brain fog and muscle cramping/stiffness. Glad to hear you're better.


Muscle cramping indicates electrolyte imbalance I’ve resolved this by Epsom salt baths, magnesium gel/oil, skin brushing. Prudent to monitor heart rate and have Calcium levels checked ie bone density, vitamin D3 and K2

Brain fog can be from SIBO.

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Funny I looked this up and it could fit. I feel my digestive system has become quite sensitive and I poss have IBS.


Advice given above from other members regarding digestion, supplementation and testing is pertinent. Test don’t guess.

A stool and or breath test might be beneficial? Perhaps also working with a Functional nutritionist who can guide you as diet is crucial. Pm me if you want a recommendation.

I also omitted to add that I take magnesium citrate (400g) 2-3 x daily as well as lots of green leafy veggies. I felt that magnesium threonate was better for my heart.

Another thing to check is a hiatus hernia and illiocaecal valve ( McBurney’s point) as they may not be functioning correctly and creating havoc.

The active hormone T3 is vital and I’ve found the reverse T3 /T3 Ratio enlightening. As it effectively showed me I was clinically hypothyroid at cell level despite the T4 numbers looking ok. Ie Conversion wasn’t happening effectively enough.

Best Wishes

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From time to time I stop taking my Levo and can honestly say that on those days I do feel better but as my GP is Deaf and will not listen to me I just plough through my day looking for alternatives to this drug and try to eat healthy

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Third day levothyroxine free and feel fine but i have to start taking them again as i dont have a thyroid gland. Be interesting to see what the doc says and how she can help offering alternative drugs.


i am sorry to hear about your pains...I am not taking Levothyroxine by choice..i have sublingual subclinical hypothyroidism with normal range TF4 and TF3 and because levothyroxine can lead to heart palpitations and i have already problem with heart rythm so i won't take it. I would suggest though to have B 12 Checked because the foggy brain and memory problem, i have had them for a while and went to see a neurologue who checked me on this and gave me B12.. after 2 or 3 months i was back to myself again ... i am older than you are...hope you will be ok..


Thank you and best wishes with your health. I'm just waiting on blood test results so fingers crossed some light will be shed on my problems.


Update: had blood tests done. The lab contacted my gp the same day to discuss. A week later I was seeing an endocrinologist who diagnosed that the thyroidectony or radiation treatment had damaged my parathyroids as the blood test showed my calcium levels were low despite vit d being ok. So I've been put on One Alpha. I've also reduced slightly the thyroxine dose but to be reviewed latter. The muscle cramps and bone and muscle aches have significantly improved so it appears this is down to the parathyroids damage. Now I wonder how long I've been deficient in calcium and why it was never monitored in the 30+ years since thyroid cancer surgery?? A lot of health problems I've experienced can be explained by what's now been brought to light ie hypoparathyroidism. Initially I was angry. Now I just want to be well and hoping now I'm being monitored that improvement will be on going. I'm glad I decided it was not normal to be feeling the way I was and go to my gp for blood tests and investigation because I've tended to just accept my health is not so good and self-manage to a large extent.


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