Thyroid UK
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Racing Heart on Levothyroxine

Hi, I was diagnosed in Sep 14 with underactive thyroid and put on 50mcg daily. At first I felt amazing on them, effects of which tailed off after maybe 4 weeks but still a noticeable improvement on how I felt before diagnosis. Then in the Dec, bloods were checked and we're still a little high, dose was increased to 75mcg. Shortly into this new dose I started experiencing a racing heart sensation. Have history of ectopic heart beats so tried to ignore those, but it's been persistently getting worse. Every day now my heart can feel like I've been running, for a few minutes or even as long as a full day, it wakes me up on occasions too.

Had cardiologist check me out and they can't see anything wrong. Wondered if it's the extra 25mcg tablets? Heard from another patient they found a particular brand to cause these symptoms. Wondering if I could try getting my 75mcg daily dose by cutting my original 50mcg tablets and having 1.5 daily. Is there any truth in this theory?

6 Replies

Welcome to the forum, SamimanF83.

It's not a myth, different makes can cause adverse effects. I found palpitations intolerable on Mercury Pharma and less so on Actavis. Wockhardt 25mcg were no problem for me.

Try your previous make 1.5 tablets. If symptoms improve your GP can prescribe [make] 50mcg x 1.5 tablets daily.

1 like

Thanks, ill definitely give it a try, these palpitations (tho harmless) are not nice 😕


Samiman, Tell me about it. It felt as if the bed was bouncing with the violence of palpitations at times.

Both over and under medication can cause palpitations and increase ectopic beats. You should have a thyroid test 6-8 weeks after dose was increased to 75mcg to check levels. Leave 24 hours between last dose and blood draw which should be a fasting test (water only) and early in the morning when TSH is highest.


Didn't know that about the blood test prep...mine has always been tested randomly! It has always been within range since the increase to 75mcg...had a few tests since Dec cause I'm getting fertility investigations as well since they found PCOS at same time as hypo...just dropping to bits since turning 30 lol!

Sam x


Sam, everything starts going south after puberty ;)

Being in range is not the same as optimal. Always ask for the results and ranges to see for yourself.

NICE recommend the TSH of women planning conception and newly pregnant should be in the low-normal range 0.4-2.0 with FT4 in the upper quarant of range. Levothyroxine is usually increased by 25-50mcg as soon as pregnancy is confirmed.


Something to look forward to...


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