Hypothyroidism and mild tachycardia: Hello, I’ve... - Thyroid UK

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Hypothyroidism and mild tachycardia

Coop20 profile image


I’ve been medicated on 25mcg Levothyroxene since August 2020, prior to that i had been experiencing symptoms of thyroid problems since 2014 really, but over the past year i have been getting palpitations on and off and have been told i have a mild tachycardia after having a three day heart monitor fitted, is this common with hypothyroidism? What can be done about it?

19 Replies

I get higher HR from being under medicated. You have been left in a stupid small starter dose. You need a thyroid blood test and then request an increase to 50mcg. 6 weeks after the new dose get another blood test and see if you need more.

Doctors only seem to think fast heart rate is associated with too high medication. But too low dose does it too for some of us.

Coop20 profile image
Coop20 in reply to FancyPants54

Hello! Thanks for your reply, so i got tested on 28th May and these were my results -

TSH - 2.69 mIU/L (Range: 0.27 - 4.2)

Free T3 - 5.0 pmol/L (Range: 3.1 - 6.8)

Free Thyroxine - 14.9 pmol/L (Range: 12 - 22)

SeasideSusie profile image
SeasideSusieAdministrator in reply to Coop20


25mcg is a starter dose for children, the elderly and those with an existing heart condition. Standard starter dose is 50mcg with increases in 25mcg every few weeks, or sometimes a patient is started on a full replacement dose based on weight - 1.6mcg of levo per kg of weight

You are undermedicated and need an increase in your dose of Levo, 25mcg now, retest in 6-8 weeks, repeat as necessary until your levels are where you need them to be to feel well.

The aim of a treated Hypo patient on Levo only, generally going by patient experience, is for TSH to be 1 or lower with FT4 and FT3 in the upper part of their reference ranges, if that is where you feel well.

Here is some information for your GP about where our levels should be:

From GP Notebook


Target level for TSH during thyroxine therapy

Fine tuning of the dose could be necessary in some patients

* aim of levothyroxine treatment is to make the patient feel better, and the dose should be adjusted to maintain the level of thyroid stimulating hormone within the lower half of the reference range, around 0.4 to 2.5 mU/l. If the patient feels perfectly well with a level in the upper half of the reference range, then adjustment is unnecessary

From GP online


Under the section

Cardiovascular changes in hypothyroidism

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

From the British Thyroid Foundation:


How can blood tests be used to manage thyroid disorders?


Occasionally patients only feel well if the TSH is below normal or suppressed. This is usually not harmful as long as it is not completely undetectable and/or the FT3 is clearly normal.

There are also certain patients who only feel better if the TSH is just above the reference range. Within the limits described above, it is recommended that patients and their supervising doctors set individual targets that are right for their particular circumstances.


Also, Dr Toft, past president of the British Thyroid Association and leading endocrinologist, states in Pulse Magazine (the professional publication for doctors):

"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 this article from Dionne at ThyroidUK:


print it and highlight Question 6 to show your GP.

Always advised here, when having thyroid tests:

* Blood draw no later than 9am. This is because TSH is highest early morning and lowers throughout the day. If looking for a diagnosis of hypothyroidism, an increase in dose of Levo or to avoid a reduction then we need the highest possible TSH

* Nothing to eat or drink except water before the blood draw. This is because eating can lower TSH and coffee can affect TSH.

* If taking thyroid hormone replacement, last dose of Levo should be 24 hours before blood draw, if taking NDT or T3 then last dose should be 8-12 hours before blood draw. Adjust timing the day before if necessary. This avoids measuring hormone levels at their peak after ingestion of hormone replacement. Take your thyroid meds after the blood draw. Taking your dose too close to the blood draw will give false high results, leaving any longer gap will give false low results.

* If you take Biotin or a B Complex containing Biotin (B7), leave this off for 7 days before any blood test. This is because if Biotin is used in the testing procedure it can give false results (most labs use biotin).

These are patient to patient tips which we don't discuss with phlebotomists or doctors.

Also, take your Levo on an empty stomach, one hour before or two hours after food, with a glass of water only, no tea, coffee, milk, etc, and water only for an hour either side, as absorption will be affected. Take any other medication and supplements 2 hours away from Levo, some need 4 hours.

FancyPants54 profile image
FancyPants54 in reply to Coop20

Did you wait and take your thyroid meds after the blood test? Was it early morning?

The aim of a person on thyroid meds is to have a TSH of 1 or below or whatever makes them feel better and resolves symptoms. If you took your meds before the blood test you may not have reliable results here. But even so, your FT4 is low and your TSH is too high still so you should ask for an increase of 25mcg Levo and retest in 6 weeks as I said before.

Coop20 profile image
Coop20 in reply to FancyPants54

Yes i waited to take my meds after the blood test I’ve always done this. My doctors are bad so with the information given I’ll try my best with them, I’m just curious as to whether the tachycardia is related i guess and I’m having dizziness as well with it occasionally.

SlowDragon profile image
SlowDragonAdministrator in reply to Coop20

Essential to test vitamin D, folate, ferritin and B12 ….likely very low if been left on ludicrous low dose

Coop20 profile image
Coop20 in reply to SlowDragon

I also do have a vit d deficiency and i self medicate this, my doctor put me on a high week dose and then told me to buy my own. Everything else seems fine.

SlowDragon profile image
SlowDragonAdministrator in reply to Coop20

Please add actual results and ranges

Being within range is not the same as optimal

Aiming for vitamin D at least around 80nmol and around 100nmol maybe better

Serum B12 at least over 500

Folate and ferritin at least half way through range

Palpitations are frequently due to being UNDER medicated

Do you wear a Fitbit or equivalent?

Helpful to show low heart rate

Coop20 profile image
Coop20 in reply to SlowDragon

Apologies, i added my thyroid results but yes here are the others…

Vitamin D - 88nmol/L (range: 50-100)

B12 Active - 48pmol/L (range: 25.1-165)

Folate serum - 3.0 ug/L (range: > 2.9)

Ferritin - 111 ug/L (range: 13-150)

I wear an Apple Watch yes and my heart rate is regularly between 80-110 resting.

SlowDragon profile image
SlowDragonAdministrator in reply to Coop20

Active B12 below 70 is considered suspect and low


Folate obviously extremely low

Have you had serum B12 tested via nhs ?

supplementing a good quality daily vitamin B complex, one with folate in (not folic acid) may be beneficial.

This can help keep all B vitamins in balance and will help improve B12 levels too

Difference between folate and folic acid


Many Hashimoto’s patients have MTHFR gene variation and can have trouble processing folic acid.


B vitamins best taken after breakfast

Thorne Basic B is another option that contain folate, but is large capsule. You can tip powder out if can’t swallow capsule

Igennus Super B is good quality and cheap vitamin B complex. Contains folate. Full dose is two tablets per day. Many/most people may only need one tablet per day. Certainly only start on one per day (or even half tablet per day for first couple of weeks)

IMPORTANT......If you are taking vitamin B complex, or any supplements containing biotin, remember to stop these 7 days before ALL BLOOD TESTS , as biotin can falsely affect test results



Low B12 symptoms


If serum B12 result below 500, (Or active B12 below 70) recommended to be taking a B12 supplement as well as a B Complex (to balance all the B vitamins) initially for first 2-4 months, then once your serum B12 is over 500 (or Active B12 level has reached 70), stop the B12 and just carry on with the B Complex.

B12 sublingual lozenges




Coop20 profile image
Coop20 in reply to SlowDragon

That’s really interesting, so i had all these tests done via Medichecks as my gp won’t do any of them, i then send them over to my doctors surgery and nothings ever picked up and as I’m so new to thyroid meds i am going by what they say and nothing has been mentioned about the vitamins of anything else.

Coop20 profile image
Coop20 in reply to SlowDragon

Also why would folate be classed as extremely low? Unfortunately none of the links will open for me?

SlowDragon profile image
SlowDragonAdministrator in reply to Coop20

You need to click twice on links to open…first page is just holding page

Folate range is 2.9 - 20

Aiming for folate at least half way through range

SlowDragon profile image

Levothyroxine doesn’t top up failing thyroid, it replaces it, so it’s important to be taking high enough dose levothyroxine

guidelines on dose levothyroxine by weight

Even if we frequently 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 eventually 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.

BMJ also clear on dose required



Guidelines are just that ....guidelines.

Some people need more …some less


Is important to increase slowly in 25mcg steps

Retest thyroid levels 6-8 weeks after each dose increase or brand change in levothyroxine

Hey Coop20. I had awful palpitations, they got worse and worse and then bang was diagnosed with Hashimoto’s a year or so later. They only stopped when I was well medicated. My anxiety which also got bad disappeared over night. So in my experience it’s definitely a sign you’re still struggling.

Your TSH is still high. Personally I need mine at the bottom end of the scale to feel ok and attempt to lose weight etc etc.

As others have said your dose is too low and will keep you feeling unwell. Definitely ask to increase it. You’ll still be in range. There’s no harm in them allowing you to try an increase.

I hope you feel better soon x

Coop20 profile image
Coop20 in reply to Cat013

Thankyou, today i feel to say the least really S**T, I’m absolutely exhausted and my anxiety is now through the roof. I don’t think i have hashimotos as i had the test for that a while back. But yes i think i need higher dose of meds to be honest but would it make that much of a difference to all of this, could it still be my thyroid problems that are causing my lightheadedness and dizzy spells and also the fact that according to the nurse last night i have tachycardia again showing up and fast bpm? I should have mentioned I’m 31 as well.

Cat013 profile image
Cat013 in reply to Coop20

Sorry to hear this. I feel for you. We sound very similar. I never suffered with anxiety or palpitations, it was definitely a symptom. 50mcg of levo helped, but at 75mcg it all went away except for when I ate sugary or high carb foods. At 100mcg with added t3 I was back to normal in that respect. Your fT3 at 5 looks pretty good so you really just need a levo increase ASAP! There is absolutely no reason for them to say no. There is lots of guidance about dosage you could take if you suspect your GP may be difficult. You are way too young to be on that dose. It’s given to children and pensioners.

As mentioned above the only other reason for some of my palpitations was sugar / heavy carbs (insulin resistance). My pulse shot past 100. That’s now completely gone as I gave it all up. Just another thought. Can’t say whether it’s relevant to you or not. Low carb may be worth a try to see if it helps a little while you’re struggling x

Coop20 profile image
Coop20 in reply to Cat013

So today following on from seeing the nurse last night my GP wanted me to go back today to have blood tests and he requested thyroid, spoke to him today and said could this be to do with thyroid meds being too low and he said no it’s not linked to exhaustion!!! This is what i hate, even though I’m telling them my symptoms it’s like they see no link to that ever. So i may have to pay to have my meds i think, i don’t even know if that’s possible or allowed?! I follow a low fodmap diet at the moment as I’m in the slightly overweight category, but doing good with exercise or i was until this all happened.

Cat013 profile image
Cat013 in reply to Coop20

Bleh. Idiots. So sorry.

This is where you need to book another appointment and go armed with NHS and especially thyroid UK information. Take the list of symptoms and tick off all you suffer with.

My argument would be that my TSH is not low so there is absolutely no harm in a dose increase or two to see what happens. It can’t hurt. It’s my body and that’s what I’d like. I’ve read enough to know there is a link so I’d like to explore this please. Don’t take no for an answer. It’s horrible and can fuel anxiety, so be calm and say what you feel. It’s your body. If all else fails tell him you’ll buy it yourself and try so it’s safer if he monitors it.

Why don’t these people ever read up on things 🙈x

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