Levothyroxine & diarrhoea: Hi, new here! I have... - Thyroid UK

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Levothyroxine & diarrhoea


Hi, new here! I have been taking levothyroxine 100 mcg since 2011. I have also had diarrhoea for the same amount of time which was diagnosed as IBS. I hate it. I’m starting to wonder whether this is a side effect of levothyroxine. Does anybody else experience this? I have no other symptoms of overtreatment, no anxiety, no tremor, heart rate is 55 bpm. TSH levels are also in range. Possible to have long term diarrhoea on its own as a side effect of levo? Thank you to anyone who has answers...

43 Replies

Have you always taken the same brand of levo? I know some have said Teva brand can give them a bad stomach.

ilkavall in reply to Hookie01

No I think I've had a few different brands. I know you're not meant to switch around but I've moved a fair few times in the last 10 years and different pharmacies end up giving me different brands! Currently taking MercuryPharma so I don't think it can be down to Teva. But thanks so much for the suggestion!

Iris16257 in reply to ilkavall

Mercury pharma is the one that upsets my stomach , I've had to ask the pharmacy to not give me that brand! Maybe try a dif brand?

Hi - I had this but it was because I was lactose i tolerant - worse still it meant I wasn’t absorbing it - now on liquid sugar free wnd fine.

I guess I wouldn't know if I was lactose intolerant so maybe this is worth a go... I have tried food elimination diets for IBS over the years, including eliminating lactose, but I never thought about my meds having lactose in! Thanks for the suggestion

helvellaAdministrator in reply to posthinking01

Teva and Aristo (100 microgram only) are the only available UK tablets which are lactose-free.

However, many do not find Teva acceptable. Hence, as you say, some manage to get levothyroxine oral solution (liquid) products.

Even then, some find the sheer amount of glycerol in them to be more than they can tolerate.

ilkavall in reply to helvella

Thanks, helvella. I will give these a go -- that should give me something to try for the next few months!

I have a very sensitive digestive system but Teva worked for me better than Mercury Pharma- I was on the loo as soon as I took the tablets till I realised what it was !


Have you had blood test for coeliac disease

Is your hypothyroidism due to autoimmune thyroid disease also called Hashimoto’s diagnosed by high thyroid antibodies

Extremely common for gluten intolerance to start or get worse on levothyroxine

Hashimoto's frequently affects the gut and leads to low stomach acid and then low vitamin levels

If you have diarrhoea you are likely low in vitamins too

Low vitamin levels affect Thyroid hormone working

Poor gut function with Hashimoto’s can lead leaky gut (literally holes in gut wall) this can cause food intolerances. Most common by far is gluten. Dairy is second most common.

According to Izabella Wentz the Thyroid Pharmacist approx 5% with Hashimoto's are coeliac, but over 80% find gluten free diet helps, sometimes significantly. Either due to direct gluten intolerance (no test available) or due to leaky gut and gluten causing molecular mimicry (see Amy Myers link)

Changing to a strictly gluten free diet may help reduce symptoms, help gut heal and slowly lower TPO antibodies

While still eating high gluten diet ask GP for coeliac blood test first or buy test online for under £20, just to rule it out first


Assuming test is negative you can immediately go on strictly gluten free diet

(If test is positive you will need to remain on high gluten diet until endoscopy, maximum 6 weeks wait officially)

Trying gluten free diet for 3-6 months. If no noticeable improvement then reintroduce gluten and see if symptoms get worse






Non Coeliac Gluten sensitivity (NCGS) and autoimmune disease


The predominance of Hashimoto thyroiditis represents an interesting finding, since it has been indirectly confirmed by an Italian study, showing that autoimmune thyroid disease is a risk factor for the evolution towards NCGS in a group of patients with minimal duodenal inflammation. On these bases, an autoimmune stigma in NCGS is strongly supported


The obtained results suggest that the gluten-free diet may bring clinical benefits to women with autoimmune thyroid disease


In summary, whereas it is not yet clear whether a gluten free diet can prevent autoimmune diseases, it is worth mentioning that HT patients with or without CD benefit from a diet low in gluten as far as the progression and the potential disease complications are concerned


Despite the fact that 5-10% of patients have Celiac disease, in my experience and in the experience of many other physicians, at least 80% + of patients with Hashimoto's who go gluten-free notice a reduction in their symptoms almost immediately.

ilkavall in reply to SlowDragon

I do indeed have Hashimoto's thyroiditis. I think I was tested for coeliac with an endoscopy in around 2012. Thank you for these links, though, I will give everything a thorough read!


do you have any actual blood test results?

if not will need to get hold of copies.

You are legally entitled to printed copies of your blood test results and ranges.

The best way to get access to current and historic blood test results is to register for online access to your medical record and blood test results

UK GP practices are supposed to offer everyone online access for blood test results. Ring and ask if this is available and apply to do so if possible, if it is you may need "enhanced access" to see blood results.

Link re access


In reality many GP surgeries do not have blood test results online yet

Alternatively ring receptionist and request printed copies of results. Allow couple of days and then go and pick up.

Important to see exactly what has been tested and equally important what hasn’t been tested yet

Far too often only TSH is tested, this is completely inadequate

For full Thyroid evaluation you need TSH, FT4 and FT3 plus both TPO and TG thyroid antibodies tested. Also EXTREMELY important to test vitamin D, folate, ferritin and B12

Low vitamin levels are extremely common, especially if you have autoimmune thyroid disease (Hashimoto's) diagnosed by raised Thyroid antibodies

Ask GP to test vitamin levels

Recommended on here that all thyroid blood tests should ideally be done as early as possible in morning and before eating or drinking anything other than water .

Last dose of Levothyroxine 24 hours prior to blood test. (taking delayed dose immediately after blood draw).

This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip)

Is this how you do your tests?

Private tests are available as NHS currently rarely tests Ft3 or thyroid antibodies or all relevant vitamins

List of private testing options


Medichecks Thyroid plus antibodies and vitamins


Thriva Thyroid plus antibodies and vitamins By DIY fingerpick test


Thriva also offer just vitamin testing

Blue Horizon Thyroid Premium Gold includes antibodies, cortisol and vitamins by DIY fingerprick test


If you can get GP to test vitamins and antibodies then cheapest option for just TSH, FT4 and FT3

£29 (via NHS private service ) and 10% off down to £26.10 if go on thyroid uk for code



Also vitamin D available as separate test via MMH

Or alternative Vitamin D NHS postal kit


Please add most recent results and ranges

Or come back with new post once you get results

ilkavall in reply to SlowDragon

Thanks for this info! Yes I have my latest thyroid function test results, although only TSH & FT4. Test done Sep 2020.

TSH: 2.4 mu/L (0.2-5.0)

T4: 21.2 pmol/L (9-24)

I've had ferritin checked last year and that was fine. Don't think I've had any others checked. I don't think I've ever had my antibodies tested before, either. I think my diagnosis in 2011 was just based on the low T4 and high TSH. Although I do remember having an ultrasound of the neck. Tough to remember everything so far back! This was in Germany as well, so difficult to check.

So some extra blood tests are worthwhile in your view? Thank you so much for all the information! So kind :)

SlowDragonAdministrator in reply to ilkavall

So yes definitely need FULL thyroid testing

Was your last dose levothyroxine 24 hours before this test?

If took levothyroxine before test the High Ft4 is false high

TSH is higher than should be on levothyroxine

Essential to test ft3 at same time as TSH and Ft4

Likely low vitamin D, folate and B12

What was actual ferritin result and range. Looking for ferritin to be at least half way through range

ilkavall in reply to SlowDragon

OK, I will order myself full thyroid test! Would certainly be interested to see the result. I will also follow your instructions about last dose 24h before test -- I've not done this before.

My ferritin result was 156 mcg/L (30-200). Will look into vit tests too.


SlowDragonAdministrator in reply to ilkavall

So only 5% of Hashimoto’s patients test positive for coeliac

But another 80% find strictly gluten free diet helps or is absolutely essential

The only way to know if that includes you is to try it

ilkavall in reply to SlowDragon

I will give gluten free a go, thanks!

SlowDragonAdministrator in reply to ilkavall

Get coeliac blood test BEFORE start gluten free diet

If test is positive you will need endoscopy BEFORE going gluten free

ilkavall in reply to SlowDragon

OK will do!

I suffer diarrhea with Levo. Endo said take small amounts frequently but that didn't help. It's been worse over the last 12 months so am now taking amino acid L Glutamine which sometimes eases the problem.

ilkavall in reply to DottysMum

Thanks for the suggestion! I have an appointment with an endocrinologist soon for an unrelated issue (low testosterone -- seems I'm just running out of hormones altogether!) so maybe I'll ask whether it's worth me trying thyroxine in divided doses.

SlowDragonAdministrator in reply to ilkavall

Are you male? Or female?

Low testosterone can be linked to being still hypothyroid

TSH should be under 2 as an absolute maximum when on levothyroxine


Replacement therapy with levothyroxine should be initiated in all patients to achieve a TSH level of 0.5-2.0pmol/L.

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)."

(That’s Ft3 at 58% minimum through range)

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 at


ilkavall in reply to SlowDragon

I am male (30y). My testosterone and luteinizing hormone dropped in 2020, which may also have something to do with varicoceles. The endocrinologist has sent me for a short synacthen test amongst other things. If I get a full thyroid profile done in the meantime then I'll be able to discuss possibility of undertreatment with them at my follow-up appointment. Thanks again for everything!

SlowDragonAdministrator in reply to ilkavall

So unless very skinny/light you’re likely under medicated

guidelines on dose levothyroxine by weight

Even if we don’t start on full replacement dose, most people need to increase levothyroxine dose slowly upwards in 25mcg steps (retesting 6-8 weeks after each increase) until on, or near full replacement dose

NICE guidelines on full replacement dose



Consider starting levothyroxine at a dosage of 1.6 micrograms per kilogram of body weight per day (rounded to the nearest 25 micrograms) for adults under 65 with primary hypothyroidism and no history of cardiovascular disease.

Also here



Traditionally we have tended to start patients on a low dose of levothyroxine and titrate it up over a period of months. RCT evidence suggests that for the majority of patients this is not necessary and may waste resources.

For patients aged >60y or with ischaemic heart disease, start levothyroxine at 25–50μg daily and titrate up every 3 to 6 weeks as tolerated.

For ALL other patients start at full replacement dose. For most this will equate to 1.6 μg/kg/day (approximately 100μg for a 60kg woman and 125μg for a 75kg man).

If you are starting treatment for subclinical hypothyroidism, this article advises starting at a dose close to the full treatment dose on the basis that it is difficult to assess symptom response unless a therapeutic dose has been trialled.

A small Dutch double-blind cross-over study (ArchIntMed 2010;170:1996) demonstrated that night time rather than morning dosing improved TSH suppression and free T4 measurements, but made no difference to subjective wellbeing. It is reasonable to take levothyroxine at night rather than in the morning, especially for individuals who do not eat late at night.

BMJ also clear on dose required



How Hashimoto’s affects men


ilkavall in reply to SlowDragon

Interesting! I weigh 95 Kg so would be started on something more like 150 mcg by these guidelines. Was started on levothyroxine in Germany, perhaps they have different rules! In any case, this is good to know.

SlowDragonAdministrator in reply to ilkavall

With Hashimoto’s we nearly always need to start slowly and increase dose slowly upwards in 25mcg steps

But your high TSH and guidelines by weight suggest you need further dose increase(s)

Many Hashimoto’s patients when adequately treated will have TSH well under one. Often below range

Most important result is ALWAYS Ft3, followed by Ft4

All thyroid tests should be done as early as possible in morning before eating or drinking anything other than water and last dose levothyroxine 24 hours before test

ilkavall in reply to SlowDragon

OK, thanks! Will let you know what my thyroid function test says and what my endocrinologist says!

SlowDragonAdministrator in reply to ilkavall

Majority of endocrinologists are diabetes specialists

ilkavall in reply to SlowDragon

OK, maybe I have to take my life into my own hands.... probably the lesson I need to learn from the last 10 years to be honest. I'm about ready for some change!

SlowDragonAdministrator in reply to ilkavall

There are good endocrinologist out there ....but if this is referral to local NHS endocrinologist, they are likely NOT thyroid specialist but predominantly see diabetes patients

As an eminent thyroid professor once said at very informative lecture.....he wouldn’t know how to treat a complex diabetes patient, so why would a diabetic specialist know how to treat a thyroid patient

Roughly where in the U.K. are you

ilkavall in reply to SlowDragon

I am in Manchester, will email for this list. Thanks!

SlowDragonAdministrator in reply to ilkavall

Not sure if any local to you on list

Some consultants are doing zoom consultations so distance no object

SlowDragonAdministrator in reply to ilkavall

But you need to work through trying different brands levothyroxine (no acacia/no lactose)

Trialing strictly gluten free diet

Getting vitamins optimal

But likely need levothyroxine dose increase too

SlowDragonAdministrator in reply to ilkavall

Email Thyroid UK for list of recommend thyroid specialist endocrinologists.......NHS and Private


Hi I was similar to you put everything down to levothyroxine changed brands was better slightly on mercury and cutting out dairy and limiting carbs however by chance had a colonoscopy which is what I'd press you to do because if I hadn't I wouldn't be here now ! Not everything is thyroid related

ilkavall in reply to karenmyring

Thanks for the warning! Guess it can be many things can't it. I feel like I've tried literally everything else though and have even had a colonoscopy a while back. The thyroid disease/medication is I feel the one thing I've not looked at. I figured levothyroxine was just a natural hormone, my docs seemed happy with my thyroid tests and I didn't think side effects while taking it were possible... But again thanks for the warning and glad you got sorted :)

SlowDragonAdministrator in reply to ilkavall

Only make one change at a time

Eg change brand levothyroxine or try strictly gluten free diet

Don’t change brand and dose at same time

Otherwise it’s extremely difficult to work out what’s helpful and what isn’t

Hi crikey that’s a long time to have diarrhoea I’m a coeliac and I checked that the Levo is GF and was told by the manufacturers that all Levo is .. But I had the same problem with Mercury pharmacy and if I remember rightly some doses of Teva.. Anyway the culprit was Merc pharmacy it wasn’t gluten it was the acacia powder that they use for a filler that is know to cause diarrhoea as soon as I stopped that brand my tummy started to settle , my niece had the diarrhoea for 3 months I asked her to show me her lev and sure enough it was the merc pharmacy .. I know lots of people get along fine with it . But for us it was the acacia powder in them . I now have on my notes Accord only .

Hope this helps xx

ilkavall in reply to lynnwin

Thanks for this. I just looked and my MercuryPharma meds do indeed have acacia powder in them. I've no idea now what other brands I've had and whether I've been having acacia powder since the beginning. Certainly something worth looking at because, as you say, 10 years is a long time and it's taken that long for me to get to the end of my tether :(

lynnwin in reply to ilkavall

Yes check the acacia powder filler was mine and my nieces problem .. also not sure if Teva has it in it too ? My niece had hospital investigations booked as she lost two stone she has been fine since changing brands but still going for investigations just to rule out .. I hope this helps for you ? I think acacia powder is used for some bowel conditions I did report it on a yellow card .. I hope this helps for you xxxx

SlowDragonAdministrator in reply to ilkavall

List of different brands available in U.K. and ingredients


Looks like Activis (Accord) Almus and Northstar 50mcg and 100mcg are acacia free

Wockhart 25mcg too

Aristo is acacia and lactose free

Partner20 in reply to ilkavall

Teva and Mercury are the two brands of levo which contain acacia. Some other medications and supplements can contain it too, so it is always wise to check anything that you take if acacia could be a trigger for you.

HiI have had this problem since taking Levothyroxine since 2009 and I actually (endo’s suggestion) stopped taking it for 6 months- don’t know how I managed to do it but did - but what I did note was this problem went away -it does include this in side effects on the information leaflet that comes with tablets.Have you spoke to GP


Do you have any other symptoms gastric reflux etc, are you taking any other medications, I am unable to take Levo, in any dose from any manufacturer. I have the most horrific diarrhoea I was diagnosed with IBS many years ago and also have to follow a low fodmap diet. They were going to investigate the possibility of SIBO, last year that got cancelled due to covid. Then recently was put on a course of anti biotics for a bacterial chest infection. Doxycycline the anti B used in the treatment of SIBO. Diarrhoea stopped bloating and gas stopped, all tummy issues stopped.... after now speaking with my gastro he feels that I’ve prob had SIBO all these years. For the first time in 15 years I’m not having to take imodium every day......

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