Thyroid UK
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what's causing palpitations when on t3 only & how is inability to convert discovered?

I was moved from NDT to Cynomel late December 2012 having been told I can't convert. I steadily built up to 3.5 tabs (87.5mcg) by April & have stayed at this dose as since May I have been extremely ill with concurrent infections- an 8 week vicious sore throat, & an unexpected asthma attack (A&E involved). Two prescriptions of prednisolone have finally helped me.

I am experiencing horrible palpitations with pulse rates of 88- 106. I know that doctors begin to worry @ 140+ but my previously normal rate was around 65. Looking back in my notes pre-illness, I see that I was experiencing a pulse rate of 88 on average. According to my carer, I would experience mild palps but then it settled down for a few days before the next mild episode.

Feeling so poorly as I do I am reducing my t3 dose to 62.5mcgs - 1 x 25 mcg tab am, 1 x 0.5mcg lunchtime, 1 x 0.5mcg but is this wise?

I am so confused. Try as I may, I still don't understand Rt3 and should I be worrying about that?

19 Replies

Sorry you are feeling like this. Today is my first day on T3 so I don't feel I can offer any help other than to say that when I was on a low dose of Armour, I began to have these pounding heart symptoms too. I cut right back, then actually came off it for a while. Until someone more knowledgeable comes back to you, I would suggest initially really cutting back on your T3, which you are doing now, and testing cortisol and iron levels. Your previous dose of 87.5mcg seems to me very high. I can recommend Paul Robinson's book Recovering with T3. It's full of really useful information.


Thank you Daisybean for a swift reply. I've tried to understand Paul's book, keep dipping into it but I find myself so confused afetre a while-brain ache!!:-)


This is an excerpt from Dr Lowe who used T3 extensively whose protocol differs from Paul Robinson's. I wonder whether L's would suit you better.

July 5, 2000

Question: I was on a fibromyalgia discussion group last night. The subject of discussion was patients who have thyroid hormone resistance. Someone posted that you believe plain T3, taken once a day, is more effective than sustained-release T3 for these patients. This seems contrary to the belief of Dr. Dennis Wilson. If you believe this, why would plain T3 be more effective?

Dr. Lowe: Whoever posted the statement was right. In my experience, for thyroid hormone resistance patients, sustained-release T3 is a poor alternative to plain T3 taken once per day. We don’t have enough evidence to know why plain T3 is more effective.

It is possible, however, that some patients have resistance due to mutations in the c-erbA-beta gene. Such mutations would result in a patient having mutant T3-receptors that have a low binding affinity for T3. (We’ve had gene sequencing on a few of our patients to identify mutations in the gene, but the results were negative. However, we’d have to test many more patients before concluding that mutations in the gene aren’t generally involved.)

Lab studies have shown that mutant, low affinity T3-receptors properly regulate gene transcription only after they're exposed to saturation amounts of T3. Under normal conditions, T3-receptors aren’t saturated, and the use of sustained-release T3 isn’t likely to provide saturation. Saturation isn’t likely to occur with sustained-release T3 because the T3 enters cells only in small amounts over an extended time.

As a result, it’s not likely that large enough amounts of T3 will reach the receptors at one time to saturate them. But plain T3 in single doses enters cells in larger amounts. These larger amounts may provide the saturation needed to provoke transcription regulation by mutant T3-receptors. If so, these saturation amounts of T3 may induce waves of transcription that on the clinical level relieve symptoms of hypometabolism

Have you also had an ECG to check your heart. I was prone to palpitations when on levo but they have gone now - all my ECG's and a five-day heart monitor were clear.


Thank you Shaws. I've been too ill to leave my bed for the last 9 weeks and am just beginning to move around a bit more. My GP has requested that I have a TSH test done because of the palpitations even tho' he knows or should remember that I'm taking T3!

I need to understand more clearly this response from Dr. Lowe. I find it all so complicated at present. I should be having a telephone consult with Dr P at the end of next week. He has always suggested dividing doses.


It IS complicated Daffydowndilly! I wish I could offer more help, but all I can say again from my own experience is that in order to stop the palps, I fealt I had to stop the meds - but that may not be right for you.

To add more confusion, P. Robinson said ... if cellular glucose levels fall, the generation of cellular energy is not high enough which can result in rapid heart rate and anxiety, So, what he's saying is having healthy blood sugar metabolism is critical. Maybe flag that up to your GP? He may test your blood sugar and at least that's something you can rule may or may not be relevant.....and of course a full iron panel would be great too (or at least ferritin) and cortisol saliva test (which you'll have to pay for yourself via a private lab....about £65) Sounds complicated, but it's just 3 tests which might really help. xx


This has been really helpful. Thank you so much. I will flag the blood sugar test to my GP as well as ask for lot are extremely nice but extremely conservative which is why it took 15 years before obtaining help from a private doctor. I've sorted the cortisol since last year and maintain adrenals with Nutri. Daffydowndilly:-)


Your comments on the dose you have changed to don't make sense to me ("I am reducing my t3 dose to 62.5mcgs - 1 x 25 mcg tab am, 1 x 0.5mcg lunchtime, 1 x 0.5mcg") but either way, it implies to me that you are taking at least 2/3rds of your day's dose in about 4 or 5 hours by lunchtime (or more?), and therefore comes as no surprise to me your heart rate is higher than it was!

When I took T3 only, I found it a roller coaster and on the advice of others had to dose at least 4x daily to get any degree of stability, and those doses needed to be a full 6hours apart.

The fact that the prednisolone helped things also is suggesting that there is an adrenal component to the problem somewhere, T3 is very hard on adrenal function. Testing adrenals won't be very representative until you are fully weaned off this though.

On T3 only, after a period you won't have any T4 left TO convert to RT3, so it won't be a problem!

I had high RT3, unfortunately I (presumably) still do, as I am unable to remove the source of it happening.. most likely chronic pain in my case, I went through the protocol to clear RT3 - it worked, after about 12 weeks; but within 6 months it was clearly coming back to much as before as the hypo symptoms came back despite my otherwise subclinical hypo only blood levels. An expensive waste of effort for me. I have settled on NDT, and doing OK, so unless there is a means of removing whatever is the source of RT3, it is always going to come back unless I live on T3 only. I wasn't in a hurry to live on T3 only if I didn't REALLY have to because of the instability I found it resulted in.


Dear Picton- thank you for this. It has made sense. I shall be following the 6 hourly routine from now & will be reducing sensibly.

The prednisolone was offered on two separate occasions, each course 5 days only. I've had viral problems since January but hatched a really vile sore throat-just that- and it has lasted 8 weeks.V.Grim.(I've had others in the past including strep throat so I know the score!) and have been mostly in bed for this time!


Picton and Daffy, have either of you tried the Circadian method for T3/NDT to assist the adrenals?


Dear Daisybean - no I haven't as yet. When I saw Dr P last year I had adrenal failure but am now stable on Nutri Adrenal (8 tabs). :-)


No, I haven't. I don't think my circumstances are totally typical though, nor did I feel I had the luxury of tie to try it out.

My adrenals are not putting out what they should be almost certainly because of long term Opiate pain drugs, it's a long known problem, but preciously little studied - similarly it's that (and/or genetics) with my thyroid issues too, so it's not likely a matter of them being able to spring back to good function themselves when the cause of their suppression is still ongoing (and has in fact been increased) - I believe it to be more than just that, as other pituitary hormones are low too, so it strongly fits what is named by a few Medics as Opiate Induced Endocrinopathy, but it's a little known condition, is even less well treated and it has been to say the least, a challenge at one point just to stay upright! I have, more recently weaned off Hydrocortisone as a trial, but I still become easily hypoglycaemic as before, just as I thought I probably would as nothing is likely to have "healed" in my case :-(

Endocrinologists have been less than useless, (even in the face of hard and clear blood tests) other than to be so obstructive to me getting well, there ignorance and dismissive attitude provided the impetus for me to do better on my own, even though initially I was so ill as to find it exhausting to do the research!

I have ended up having to seek treatment for what I can privately, with support for prescribing on that basis from my more supportive GP (mainly related to the Hypogonadism, thank God it's the most expensive component!) and I self-treat the rest on an ad hoc basis (sub-clinical hypothyroid and rock bottom adrenals mainly) based on long tried and tested protocols for hypothyroid and adrenal fatigue more widely used in the US. I didn't have the luxury or enough well-being left to trial more vague and less robust methods, as even without these problems with my pain and disability it's about all I can do to look after myself!

If I had the overall well being and the strong financial backup I wouldn't be trialling that anyway, and would be looking to trial using a method supplementing large doses of transdermal pregnenolone plus thyroid hormones to increase metabolic rate, to provide the hormones that are made from that "mother hormone." However it too is somewhat untested on a large scale, hasn't been tried at all for my circumstances and therefore not something I have felt able to risk when there are methods that have been used successfully for decades, and above all are cheap to implement, (forever is a long haul!) and widely found to be safe.

Few hiccups, but so far, so dramatically good, I am still here more than two years after what I thought I would get to less than 4 years ago when I was virtually housebound! I was so ill I was thinking suicide while I still had enough strength and the drugs at hand to do it! Add in a Low carb diet, and I am also 52kg lighter to haul around, as well as 100% in control of the hypoglycaemia I was suffering from low adrenals and insulin resistance!



I began T3 in November and my experience has been similar to yours (without the illness). A couple of weeks ago I rang Dr P in desperation and he said I have been overdosing. At that time I was on 125 mcg. He said I should reduce it slowly and when i asked him for specific instructions he said to take half a tablet (mine are 25 mcg tabs) less. Then stay on that dose for a week (even though I might still feel overdosed). After a week I should reduce my dose by half a tablet again and continue for another week. Then again and again, if necessary, until I was on the right dose. I think he felt it was safer to reduce the dose slowly.

He said that all the time I was doing this I should keep taking my pulse and temperature and recording them and my symptoms because that would give me an indication as to what was happening.

I felt quite different by the end of the week. Following Dr P's instructions meant I was not forever changing the dose because I felt ill and I think this period of stability helped. I am still not right. I have reduced the dose by one whole tablet now and tomorrow I will reduce it by another half a tablet. At first my pulse, which had always been low like yours, was up in the 80s and 90s. By the end of the first week it was in the low to mid 80s and now it is down into the 70s and 80s so I can see things are progressing well. My temperature was up as well and that too seems to be coming down although not as obviously as the pulse.

Hope this helps you. Good luck.


Thank you very much mstp. This has been very helpful & comforting. I have misunderstood Dr P in the past. I started on half tab Cynomel in November & from my notes of the time somewhere in Dec I had arrived at 1 + 1/2. He stated there was 'room for manouevre' so I increased by another 1/2 =total of 2 tabs. He also suggested that I could increase very slowly which I did.

I've obviously got things wrong so will reduce and keep a check on temps & pulse!

I wish you luck too. :-) Daffy


Presuming correct understanding 87.5 mcg of T3 sounds depending on your body weight like quite lot of hormone DD.

There are factors that throw off the rule of thumb estimates for this though, so it's hard to know.

It'd sound especially like a lot though if you were not spreading it over the day, and instead taking it in large lots.

Applying the x3 or x4 rule of thumb that could be equivalent to roughly 260mcg to 350mcg or more of T4.

My suggestion would be that you need to talk to your doctor.

My own experience with T3 (but who knows how others may react) suggests that starting low and slowly easing up the dose in small steps over many weeks is a good way to zero in on what works.

An increase of the equivalent of only 50mcg of T4 or 10mcg of T3 is more than enough to produce definite changes in how i feel once i'm reasonably close to what's needed - it'll very definitely tip me over the top and into a raised pulse (up by maybe 5 beats per min) /feeling a bit over replaced if I'm already there.

Even a very small change like 5mcg of T3 (1/4 tab) or 25mcg of T4 is likely enough to have some effect once I'm close.

It's hard to do this in a totally structured way in that it tends to come down to getting the doctor to co-operate in adjusting the prescription.

If you're considerably over or under replaced it can be very tough to tell what's going on - not to mention that it's potentially risky.

It'd be down to your doc, but if either was likely the case i.e. I was 'lost' my inclination would be to drop the dose down to a safe level calculated on my body weight and see how i felt - with a view to working up from there if the symptoms suggested that it had left me a bit hypo.

There's rule of thumb numbers all over the place for this, but they are pretty approximate and it's not unusual to need to ease up from them...



Hi vajra! Thanks for responding with so much detail. I hadn't realised that body weight plays a part. Can you explain that a little please?


I am not convinced it is a lot of use though, other than for initial commencement of dosing, (you have to start somewhere!) for one thing, it does not take into account such things as remaining thyroid function, nor any resistance at a cellular level!


My suggestion would be to seek out a thyroid friendly doctor - especially if you are not easy with numbers DD.

Here's a thumbnail non-expert collection of views on some of the hypothyroidism related issues you mentioned. It's rather more than a 'little', but it's a bit like pulling a thread on a woolly jumper.

There's variants of the weight based calculation that get used by doctors and others, but this page is fairly typical of the sort of approach used to calculate a replacement dose of T4 hormone:

You'll notice that there's various allowances for heart disease and other conditions - and most doctors will start patients a bit below this sort of level and work up to it. (even though it's for most people fairly conservative)

Practitioners tend to take no chances if there is any suggestion of heart trouble about and will start quite a bit lower again in those cases. It's anyway not unusual to be left on very low doses of hormone by very cautious doctors - to the point where we end up hypothyroid and feeling rotten.

In practice as this paper suggests there's quite a bit of inaccuracy in this rule of thumb for some:

It's very possible (if seemingly fairly rare) to get into quite serious trouble as a result of taking too much hormone, especially if we have certain underlying illneses like those mentioned in the first piece - so common sense caution and a methodical approach are important.

You mentioned diagnosis of conversion issues.

This piece covers most of the territory described here:

The classic 'poor conversion' scenario i guess is where a person is prescribed what should be an adequate dose of T4, their TSH is by the blood test well suppressed and yet they continue to show hypothyroid symptoms. Doctors instead of diagnosing a conversion problem in this case often refuse to accept the possibility of thyroid illness - and put the symptoms down to various supposedly separate illnesses like depression, fibromyalgia or whatever.

This was where I was for many years. There's reports about that suggest that at least 1/3 of hypothyroid patients fall into this sort of scenario.

The classic conversion problem occurs where for whatever reason (genetic predisposition, nutrtional or vitamin deficiencies, gut problems, adrenal exhaustion, toxicity etc) the patient is unable to make enough T3 (the active form of the hormone) from the T4 they are taking. The thyroid makes some T3 anyway, so hypothyroidism due to poor conversion may worsen after a thyroidectomy because this capability is removed.

Taking some T3 with the T4 can often overcome this issue, but it can take a while to sort out exactly what proportion and quanties of T4 and T3 suit an individual best.

One to bear in mind is that if using the body weight rule of thumb to calculate a starting dose of hormone then T3 is handled differently to T4. (see Townsend above) T3 is commonly regarded as being roughly four times as potent as T4, so that each 4 mcg of T4 calculated as being required using the body weight method can be replaced by roughly 1 mcg of T3. e.g. 100mcg of T4 is roughly equivalent to 25mcg of T3

It can get very controversial in that some report doing better on more hormone (especially more T3) than the weight based rule of thumb might suggest - there's a view (opposed by most doctors) that extra T3 over and above that suggested by the body weight rule or the recommended TSH range may 'bounce' the system into using hormone by overcoming issues with dysfunctional receptors and the like.

The major reason for caution in this case is the risk of side effects like stressing the heart, or loss of bone density and the like - issues which could potentially 'come on' quite quickly if the body suddenly becomes able to use the extra hormone.

Another issue reported is the possibility that taking more T4 than the body can use can lead to the T3 produced being the inactive 'reverse T3' form. In which case the patient's bloods will test OK for T4 and T3 - unless reverse T3 is specifically tested for.

A final cause of controversy is that blood T4 and T3 levels and the associated metabolic processes that use the hormone are regulated by different mechanisms - and there's considerable disagreement about exactly how they work, what's 'normal' and how they interact.

What seems to be becoming clear is that TSH relates primarily to T4 levels in the blood, and at that only in the brain area - so it's not regarded as a reliable indicator of thyroid health by many progressive practitioners. Most doctors are very reluctant to accept this because of the guidelines issued by one of the major US endocrine associations.

T3 is not a magic bullet. it's possible to have correct quantities of T3 (and T4) in the body and not be able to use them because of problems like toxicity, vitamin and mineral deficiences, gut problems, genetic predispositions etc - and so still be hypothyroid and ill. Resolving issues like these often requires a holistic approach to whole body health - and lots of trial and error and intuition - and hence time.

Too much hormone is one obvious possible cause of palpitations, but there are other scenarios often associated with them too which others more expert may be able to talk about....



I am overwhelmed by your kind efforts on my behalf. I've had to read & re read-(foggy brain!)-as well as clicking on links. I've made some notes.

I am with Dr P but I've realised that I need to get very specific instructions from him. I've made a huge mistake and must now reduce T3 very slowly. When I was taking 1.5 Cynomel daily my pulse was around 62. DrP said there was room for another half.

I may have misinterpreted his suggestion to further increase and have ended up in this state!

Many, many thanks once again

Daffy :-)


No prob D, hope it's helped. Bear in mind that I'm no expert - and double check more sources. It's really important that we get to the point where we know what's going on, and become able to play a very active part in managing our own replacement.

Most of the above thinking has seemed to check out pretty well in my own case.

I was a classic case told for many years that i was normal based on the stock blood tests - when actually as a result of probably poor conversion I was badly hypo and had advanced thyroid auto immune disease plus a range of other related conditions and symptoms. T3 proved essential, but it's taken years of diddling about to get it tuned to where it is and it's still not 100%.

My apologies to the other guys if I managed to repeat lots of what they said - i was just trying to set it down in a single piece.

Picton hit it on the head regarding the use of the weight rule of thumb to calculate starting doses. It actually isn't so far off for me, but some end up miles away for the sort of reasons she said and i also described in slightly different language.

The one that's tough is if we end up a fair bit off - it can be quite difficult to tell whether we are high or low unless the situation is pretty gross. My personal preference is to try to approach a correct dose by degrees from below - basically because it's safe and because i've got familiar with what a tiny bit too much hormone feels like.

Depending on who you talk to some don't worry too much about taking a bit too much hormone, while others become very concerned. I don't in truth know what the risks really are, but suspect that short of seriously overstepping it that a moderately raised pulse isn't a big deal for a basically healthy person.

I wouldn't want to let a situation run where I was significantly overdosed though...



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