Palpitations: how can you tell the difference between too much t3 or dose wearing off?

I've suddenly had to start taking more t3 - it seems to wear off so much earlier than normal - so I've added in a third dose (just a quarter of a tablet). About two hours after that last small dose my heart has been beating faster than usual.

Does this mean I'm getting palps from the t3 wearing off rather than from taking too much t3?

I'm assuming if I was on too much I'd start getting palps soon after taking my dose - ? No other hyper symptoms. I'm shattered at intervals throughout the day and feel my energy return after I've topped up with a little t3.

59 Replies

Do you know if your magnesium and progesterone levels are optimised? Jane x

Good question Jane. I haven't had them tested in a long time. I do use mag oil in my deodorant and have recently started taking a Floradix supplement which includes magnesium. I briefly (for two or three months) tried transdermal progesterone cream (doc thought it might aid my recovery) but this was a few years ago. Stopped using it when it finished as it didn't seem to make any difference. x

Punctured bicycle, I think that levels peak a couple of hours after taking it - that's my experience anyhow. If your levels have been low you might be more sensitive to it than usual. I was told that the half life for T3 is 3 or 4 hours, so it's not likely to be wearing off after 2, I don't think. I do wonder if changes in the weather is messing us all up.

I guess I was thinking of the various amounts I'm taking and how it seems that they wear off differently depending on how high a dose I take. I take 18.75mcg t3 at 6 in the morning along with 75mcg levo, and I used to be okay until late afternoon, but recently it seems to wear off by noon. Then I take 12.5 t3 as an afternoon dose (today around 1) and this evening I took another 6.25 around 5.

So I've done a back of the envelope calculation and figured the first dose took 6 or 7hrs to wear off, the second took 4hrs and the third took 2hrs. (When I say 'wear off' I just mean that moment when I start swearing to myself and thinking about a nap.)

Am I wrong in assuming if I take a small dose it will wear off sooner than a large dose?

I don't think so, that's where it gets really complicated though. The half life is the time it takes for half of it to disappear but then it's half of what's left (1/2) that goes over the next half life (leaving 1/4 of original dose). So if half life is 4 hours and you take 20 (to keep maths as simple as possible). There's 10 left after 4 hours and 5 left after 8 hours, and 2.5 left after 12 hours. So when you later doses it's sort of accumulating isn't it. That's why it's so flipping difficult to get it sorted!!! I take my Levo at bedtime and feel as if I need my T3 by morning. If you're taking your Levo in the morning won't this be dropping by evening too - how do you get through the night? Levo definitely works better for me overnight than in the daytime, have you tried it in the evening? I think I can convert it better at night as I'm not stressed. I also worry about reverse T3 if I take Levo when I've got lots of T3 circulating. The other thing is - are you sure that when you're swearing at yourself and needing a nap that it's not too high? I say this because I've found that evening tiredness can be due to me taking too much, but it's quite hard to spot at first. Is swearing at yourself like irritability? For me this is also a high sign ... I sometimes think I'm going nuts trying to work this out :)

I have taken levo at night and at the time it helped me sleep better so I carried on until something - blood test, eating too late etc - meant that I had to take it in the morning and carried on. I now sleep really well and wake up really well so haven't found a reason to change it. :-)

When I was potentially overcorrected (and this is contentious because due to circumstances I had blood drawn after taking my morning dose) my only symptoms were a bit of borderline diarrhoea and trouble 'switching off' at night. I felt well and had stamina and strength, which I'm lacking now.

When I said I was swearing to myself I meant that I often hit a wall of tiredness and find myself walking around trying to do stuff in such a fug that I find myself swearing, like you might if you had a headache or hangover. It is relieved with a small dose of t3 but often returns within a couple of hours.

Like you I feel like it makes me crazy trying to work it out. Even if I spring for a test, how do I know it is accurately reflecting what's going on? When I had my last tests I had two done within 36hrs of each other (one nhs and one private). The one taken after I was off meds for 21hrs was within range and the other one (to stay upright I took a tiny dose of 12.5mcg t3 9hrs before the test) showed high t3.

I despair. :-(

Sounds like your levels are low then. Perhaps the palpitations are due to sensitivity to the T3 at the moment or early dropping off of levels? Some seem to think this can be due to mineral deficiencies - I don't know anything about these and have got through so far without any tests except one for Ferratin which was good. Would be interesting to know what tests say but as you say they're so vulnerable to timing of dose. Hope you have a good day somehow

Looking forward to getting my test results for iron, ferritin, etc. Hopefully it will be illuminating.

I need to sort out a different doctor as mine is so awkward to get in touch with. Will organise tests as soon as I have someone to interpret them.

I think as I haven't got much on today I'll put off or skip my afternoon dose to see what happens.

May I ask what you do when it comes to tests? How long do you leave between your meds and blood draw?

Thanks again for your help.

I take Levo as usual the night before (50) and try to have test as early as possible and take T3 immediately afterwards. Whatever I do there is seldom measureable TSH but medics take more notice of T3 and T4 or how I feel. (If I'm feeling well they're tending to leave me alone now, as I've been really poorly when they try to bring me in range)

Hi To be honest I do think that means you are on too much T3. it is important to split thae dose to 12 hours apart, which I am sure you know. I would also be sure to have a blood test, TSh, T4 and FT3,only wy to be sure about the thyroid. T3 does effect the heart very much. , too high or too low.

Best wishes,


Hi Jackie. Not everyone splits their dose, or takes it 12hrs apart. My doc said 6am and 3pm. I'm on almost half as much medicine as I was when I felt well because I had a hypo/hyper wobble out of the blue, so I'd be surprised if it was too much, but anything is possible.

Jackie, how long do you wait between taking meds and having a test? That is the part I'm struggling with (as above).

Hi Not sure which you ask, so to answer both ways.The FT3 does stay up for about 12 hours after taking meds I know this from both my Endo and when tricked" into a thyroid test while in hospital. You do have a high 2-3 hours after any T3 why it is best to split. I also s[lit my armour ( on both) as I find it makes me more stable glo because f the T3 content.

The other answer, is any change in meds should be followed by a blood test after 4-6 weeks. Levo and T3, being synthetic both take longer to be fully in the blood stream.Same in reverse too.

If on beta Blockers, never take before, in the morning of a blood test, as false result.

As I am sure you know, the slightest thing can cause a wobble in thyroid, if possible best to ride it out.


I think it's very individual Jackie. I take mine 5 hours apart

Palpitations are one of the side effects of Levo it says on the leaflet if you get them that you should see your doctor. Let him be the judge.

Sadly my gp wouldn't take the slightest notice, which is why I come here. Particularly since my heart rate is within the normal range I can't see what even my private doc would do except take me off t3, and I often get palps when undermedicated. It is tough to know sometimes which side of the line you're on, but in my experience the docs are not necessarily more informed.

I ve reduced my T3 this week and my palpitations have now gone - I think the weather causes me to need to change the dose

Very possible. Last time I had a wobble (from hyper to hypo on unchanged meds) it was in Oct. I had also just returned from a six-week trip abroad in a much sunnier climate. There was a gap of about two weeks when I felt okay after returning, and then I became hypo.

I often wonder - esp with the vit d connection - if there is some link between sunshine and thyroid. I know people have thyroid issues in sunny climates, but I wonder if a change in exposure to sunlight can effect how you process your meds.

I agree :). I've had big problems in the past after returning from travel to warmer climates. There's also the problem of adjusting meds for time change.

Try reading this page it's been a big help on understanding T3 and the half life etc. :-

Thanks for that but for some reason the hyperlink is incomplete.

I left the http off the beginning as some forums don't like links posted - if ever your stuck again try copy & pasting the link it will automatically add the http for you - I have added the whole link this time. Some good information on T3

Thanks - it works now. :-) I've skimmed it but I'm looking forward to reading it properly.

The way this site treats a link - makes it into a hyperlink but only the first part is visible - you can't copy/paste. Would be good if you could make the hyperlink yourself because if it went wrong you could just leave it as text for people to copy and paste, but it automatically fades out the address as "..." and hovering doesn't reveal the link.

I'm getting palpitations too but I'm only on levothyroxine (50mcg). I have been on this dose for 7 weeks but heart started racing on Saturday after taking my pill. (Typical, the day the docs surgery is closed). Saw him this morning and he says it is very unlikely I'm overmedicated on this dose, especially as problem only just started. Any ideas anyone?

GP gave me a form to get an EGG done as I have had chest pains in past (had chest x-Ray last year and it was clear) but can't get there until Thursday or Friday as no transport before then.

Good luck. I hope you get it sorted out.

Thanks, you too.

I didn't take my afternoon dose of t3 today and I feel as hypo as ever even though my pulse is still slightly higher than normal. I'm wondering if palps are in this case a hypo symptom.

Keep going punctured bicycle, you will get it sorted. I suppose it could be so high that missing one dose hasn't brought it down yet, or perhaps you'll be able to tell a few hours later. Have you tried taking a fraction of a tablet more to see if it makes you worse or any better? Good luck.

Thanks. :-) Yes, I did that on Sat and Sun, took an extra tiny dose in the evening when I felt tired. It does relieve the fatigue, which I think indicates that I need it.

For what it's worth, I think something else is at play here, maybe it's a vitamin/mineral issue. In my experience diarrhoea is a telltale sign for hyper and that was fine so I doubt I was very high.

I missed out a dose yesterday and this morning I took my normal dose and am feeling hypo - tired, ears ringing, that awful lumpen feeling and a feeling like I have a heavy weight on my head - but I bet if I took a test the results would look good.

I'm sure it will all be fine but I feel sad when I think that this time last year my journey with t3 was beginning and I had it all to look forward to. :-(

Why sad?

Because I felt so good - then great - for about six months, I started exercising, I was strong and had stamina and it made me feel so optimistic. Now I feel I'm back in the forest again.

You're only at the edge of the forest, you just can't see how to get out at the moment, it will come right again. Keep spirits up. (Perhaps my dose change wasn't so successful after all - as I'm writing this at 3.45am...) :)

Bless you, thanks for your encouraging words. Sorry to hear you didn't have a great night's sleep. I hope it's just a matter or a tweak or two before you are sleeping like a baby. :-)

Thanks :)

Why don't you try taking all your meds in one dose again? If you can stick it for a couple of days the flooding of your cells might resolve the palps you get by taking bites of T3 throughout the day.

Thank you Clutter. Funny, when I was putting out my meds last night I had to think for a long minute about whether to do just that.

I may do that tomorrow. I just feel all at sea now.

Hi again. I took my whole dose (or what passes for a whole dose at the moment since I don't know if I need more or less) at 6 this morning and my resting pulse is for the moment the same as always.

Since being on t3 it has been higher than it used to be - generally 80, occasionally rising to 90 - but that is within the 'normal' range so I'll take it. I'm spectacularly unfit at the moment having been utterly sedentary since the end of Oct so perhaps once I feel better and am more active it will get better.

Thanks for this suggestion. The first time I experimented with it I found my energy levels were much more stable so maybe it will help me out again.

Try and stick with it for a few days. Once your cells are enriched with T3 your system might balance/stabilise and an additional nibble won't be so 'felt'.

I hate to chop and change but I felt so dreadful yesterday and unequivocally hyper in the evening that I skipped my meds entirely this morning. I feel like I need to reset it all.

I had skipped one dose of t3 and that didn't help at all so I worried that I was extremely high and thought I'd try taking nothing today. The worst that can happen is that I will be tired but I'd rather be hypo and tired and build up to feeling well than be hyper and tired and just overmedicating daily.

That's a shame. Have you thought about increasing your T4 and reducing your T3?

That is a completely sensible proposal. I must own up to feeling upset just thinking about it because I felt so unwell on t4 alone and only got any life back when I started taking t3. So whether or not it's valid to feel this way, it makes me feel like I'm going backward. Also, I remember having to start taking more t3 in the morning just to get up - I had been on 12.5 in the morning and again in the afternoon and I started to really struggle to get up in the mornings, which resolved when I added a bit more to the morning dose. I wonder how I will feel on even less.

I accept that this condition can be kaleidoscopic in that it is constantly changing almost in three dimensions and what failed last year may succeed wildly tomorrow. So maybe it's time to try again.

I feel tired and weak today but not as falling-over exhausted as I was yesterday. It will be good to acquaint myself with how it feels to know I'm a bit hypo so I can use it as a gauge to measure how I feel in future.

I wish I had a good doctor. I hate trying to do this all myself. I'm just not up to it.

Thanks for your help. I really appreciate it. :-)

You may have been very depleted in T3 when you first started using it, hence your initial sense of well being. You may not have been converting T4 well and replenishing T3 has enabled you to convert well. Now, perhaps, you need less as it's making you feel hyper.

Supplementing vits and minerals may also mean that you're in better nick and need less. It may be that you need to increase your T4 and reduce, perhaps even stop your T3 for a while and reintroduce it if/when you feel the need for it.

It was stopping meds to allow my system to clear of the build up from over replacement that enabled me to reintroduce and tolerate T4. I don't suggest this is the answer but it is worth thinking about in respect to T3 which is probably easier to stop and start than T4.

If you still have your thyroid perhaps it's trying to be useful and is interfering with your meds.

Yes, I think this is a certainty (thyroid is trying to help) as this time last year I was on 150t4 and within a few weeks of trying t3 I had upped it to 10mcg and felt great. Eventually t4 was reduced to 125 and t3 increased to 25. I was on this until I began to feel unwell in Nov and doc reduced meds due to hyper symptoms. Despite tests being normal I've felt unable to raise meds since due to palps so I'm now on 25t4 and 35t3, which in relative terms is just a crumb of what made me well last year. It is possible that I've now gone hypo again. I have no idea. I need to be tested.

I'm no longer on all my supplements so if anything I may be compromised in being able to use my meds. I stopped supplements a few weeks before blood tests and only partly started them again because I had another lot of blood tests recently (b12, d, folate, iron, ferritin) and didn't want supplements to interfere.

I'm so tired of trying to figure this all out and feeling ill. I'm tempted to stop everything and start again but I suspect the symptoms will be upsetting. I've finally got my hair back and my gut is working well and I'd hate for it all to go pear-shaped - or should I say *more* pear-shaped.

You don't know how helpful your comments and support have been. I feel like I'm out here twisting in the wind and have no one to turn to. I'm utterly perplexed about how I feel and what it means.

First thing tomorrow I'm going to ring the gp and ask if they'll do a blood test for me. Otherwise I'll book in a private one.

Thanks again. x

If your gut is now working well then your absorption will have improved and you may well be over replaced but that doesn't account for ongoing symptoms, unless they're due to you stopping supplementing. I hope the blood test helps to explain where you're at :)

Well 'working well' was a euphemism for no constipation :-) , so I don't know how my absorption is affected but I would be really unhappy if I messed about with my meds and ended up constipated again. There seems to be no remedy for hypo constipation; it's such a menace.

I was really constipated, and was really concerned about taking iron too and making it worse, but high dose vit C has resolved it despite the iron. Might help???

Many thanks. I'll keep that in mind. When I get the hypo variety of super-constipation none of the usual things work very well but I haven't tried vit c.

I use Redoxon 1000mg with zinc. Fizzy orange tablets that you drop into water.

I find the hypo constipation scary - I have sometimes thought I would have to go to hospital with it. There's some good suggestions for resolving it here

Omg it's just awful isn't it? It's so difficult to resolve. Some stuff 'works' in a sense - flaxseeds are good - but it isn't really sufficient. When my meds are good I'm fine. In fact that's one of the ways I can tell my meds are right.

...wondered if Paul Robinson could help with the T3. He is a member of this forum and very helpful. His website has good information on the blogs Blogs - his included....

Many thanks. I've sent a request to join the fb group.


Have you tried rearranging the current dose rather than changing it? Eg increase morning dose and lower another later in the day?

Yes, have been taking three quarters in the morning and one in afternoon but still so tired and worried that I'm over rather than under.

I was on Thyroxine for over a year without success then I persuaded GP to prescribe t3, 20mg morn and eve.

I have been on only this for 3 months and have booked a blood test for Tuesday 10.30.

I plan not to take my t3 that morning but reading replies above I wonder if I should miss out the evening before dose as well? Please advise.

For me, taking a little t3 about nine hours before my test meant I was over (high t3). I had had the same test the day before and left 21 hours between my pill and blood draw and that one was fine. I don't know if there is a definitive approach to give you 'correct' results.

Thanks, I will leave off the dose the night and morning before the test. I don't want GP to lower my dose.

Good luck. :-)

This is a really long chain of posts and it's really slow to load on my ipad, and I can't tell if I'm reading the most recent posts at all. Very interesting though. :)

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