Why T3 (Liothyronine) Should be The Last Hypothyroidism Treatment That Patients Consider

I developed Hashimoto’s thyroiditis (an autoimmune thyroid disease) around thirty years ago. I suffered during the early years as is so common for thyroid patients.

I was given the standard T4 (Levothyroxine/Synthroid) thyroid treatment. However, when I was told my endocrinologists and doctors, “You are cured!’, I asked them, “Why do I still have all the symptoms of hypothyroidism?”

The answers to the question were varied depending on the doctor I spoke to:

  • I was told I had some unknown disease that appeared to have symptoms reminiscent of hypothyroidism.

  • I was told that I had a psychological problem – possibly depression.

  • I was consistently told I could no longer have any problems with thyroid hormones because my thyroid hormone levels were ‘normal’ as determined by laboratory testing.

  • I was asked to join a growing number of patients in an ME/CFS support group by one endocrinologist. I believed that since these were thyroid patients with symptoms of hypothyroidism (or ME/CFS), this simply meant that my endocrinologist was happy to stick a label on me and push me into a room to commiserate on my bad luck and lack of a future with others that he had failed to help.

  • I was refused any more blood tests or referrals by one GP unless I took Prozac (antidepressants) for some time.

The quality of the treatment I received from some of these ‘doctors’ seemed to border on abuse.

Far too many thyroid patients who do not feel well on just T4 thyroid hormone medication have encountered these ridiculous attempts to justify poor diagnostic work and even poorer treatment.

So, I did my own research. I read endocrinology books – real ones that are used during medical training. I bought books that I could not find or borrow. I used the emerging Internet resources.

I concluded that a trial of T3 (Liothyronine) was necessary because my hypothyroidism was not fixed by using Levothyroxine (T4).

This was needed at the very least to see if I could learn more about what was ‘broken’ inside of me. I knew something was broken because such a wide range of T4 dosages had been tried and had all failed. I also knew that this had all occurred after the advent of my autoimmune thyroid problem – Hashimoto’s thyroiditis. I was totally healthy prior to this point.

Eventually, I found a doctor who allowed me to try natural desiccated thyroid (NDT) and then T4/T3. We also used hydrocortisone and prednisolone. None of these treatments made a bit of difference. Then eventually I got the T3 trial that I had wanted for so long.

With T3, the lights went on. Within a week I could get up the stairs at home more easily. My digestive problems all vanished within days. I began to be able to think clearly and function once again. Within a few weeks I felt like I was a different person – not the shambling wreck of a human being, old before his time. T3 on its own was the answer and the clue. I still had a lot of fatigue issues and these arose from my continuing low cortisol, which I still had to resolve.

My problems had definitely been occurring at a cellular level and beyond the ability of any blood test to see them. 

I now know that there are many causes for this. Although at the time I was not really able to pin down any one specific reason.

It took me nearly three years to completely finalise my dosage and understand how to use T3 correctly. I had to apply all my background in science and applied research to understand everything I needed to know to get to grips with T3. I had to raise my cortisol levels a lot to really be able to properly recover.  However, It was worth it.

I have now been using T3 (Liothyronine) for around 20 years and am fit and well. I have no weight issues or any other symptoms of hypothyroidism or low cortisol.

So, why have I chosen the title for this blog post? It is simply that T3 is more difficult to find the correct dosage for than other treatments, and that doctors are far less keen to prescribe it.

When I first began to discuss T3-Only use on forums many years ago, I frequently met ignorance, defensiveness, incredulity, and even abusive and rude comments from other thyroid patients. There was so little discussion about T3 and so few people who had good experiences of using it that I found the Internet forums to be quite difficult places to inhabit. The situation is somewhat different today. More and more thyroid patients in the UK and the USA are using T3 to get well.

Over the years I have now spoken to thousands of thyroid patients who have managed to recover their health using T3-Only.

Many patients are now hungry for information about this under-prescribed thyroid medication.

However, increasingly I get questions from people who want to know if they might be able to get well by taking T3-Only instead of T4. Some people even consider switching directly from their current T4 medication to T3. This increasing trend has provided me with the title of this short article.

T3 is not an easy drug to use and any patient or doctor who begins to introduce T3, whether on its own or in combination with T4 or NDT, must know quite a lot about it before commencing its use.

Some of these thyroid medications are more difficult to use than others. I believe that the order goes like this (with increasing difficulty):

  1. T4 (levothyroxine) – easiest to use.
  2. T4 / T3 in combination.
  3. Natural desiccated thyroid (NDT).
  4. NDT / T3.
  5. T3-Only (T3 on its own or pure T3) – hardest to use.

I am prepared to debate where 2 and 3 are relative to each other and possibly even 4. What is clear to me is that 1 (T4) is definitely easier to use than 2-4 (combos of T4 and T3). Number 5 (T3-Only) is harder to use than the others. 

Why should I say this last statement?

Once the nature of the T3 hormone is understood and the reasons why people resort to it are also taken into account,  it should become clear why T3 is a medication that should be not be seen as a simple panacea.

In the human body, the biological half-life of T4 is approximately seven days, which means a patient can take their entire daily dosage of synthetic T4 in one go, without any issues, because it is used up relatively slowly.

In contrast, the biological half-life of T3 is believed to be twenty-four hours. However, a single dose of T3 is rapidly absorbed and reaches peak circulating concentration in just two to three hours (2.5 hours is typical), after ingestion.

Blood serum concentrations of T3 may remain somewhat elevated for six to eight hours. After this, blood serum concentrations decline again, unless another dose of T3 is ingested.

So, for most thyroid patients T3 has to be taken several times a day. Taking it all in one go, once a day, is far to potent in one dose for most thyroid patients.

The other interesting fact about T3 is that it arrives in the body extremely quickly and it has the effect of rapidly suppressing the TSH. Therefore, patients who are receiving only T3 replacement therapy should expect unusual laboratory tests of thyroid hormone levels. This makes it impossible to use thyroid lab tests to manage the T3 dosage. Many doctors are still very uncomfortable with this as they mistakenly think that the lab ranges developed for people on T4 meds can be used for ALL the thyroid medications.

Low FT4 levels should be expected. FT3 results could be low, normal or elevated above the top of the reference range, depending on how much T3 is being prescribed and the exact time of the thyroid blood test, in relation to the time that the last dose of T3 was taken. TSH could be highly suppressed or at the very least TSH is likely to fluctuate far more with the use of T3 medication than with T4.

The above information, on the rapidity with which T3 achieves peak serum concentrations and then declines again and the potential for unusual TSH, FT4, and FT3 results, is very important. This means that laboratory tests cannot assess the adequacy of replacement with T3.

Endocrinologists, doctors and thyroid patients may wish to use thyroid blood test results to check the T3 dosage – but this simply will not work!

Patients that are using T3 on its own will certainly struggle to get any value at all from thyroid blood test results. Those that are using T3 in combination with T4 may also see some distortion of their thyroid blood test results depending on how much T3 is being used. This means that other methods need to be used to manage the T3 treatment and set the correct level of T3 medication. Symptoms and signs must be used but this is not as easy as the conventional way of looking at thyroid labs.

In particular, it is critical to be aware that people who use T3 are taking it because something in their normal processing of thyroid hormone has broken.

All we can see is that T4 or T4/T3 does not make someone well but that T3 does. It is crucial to realise that in this case the T3 is being taken to overcome whatever the problems are and that all that is important is that the patient feels well and that normal symptoms and signs are returned (including key measures like blood pressure and heart rate).

In order to achieve this, the right amount of T3 needs to be effective within someone’s cells. When this occurs, the levels of hormones within the bloodstream are likely to be completely unrepresentative of the cellular activity of the T3. So, TSH, FT4, FT3, or reverse T3 in the bloodstream (which is the only place they can be measured currently) are very likely to be unrepresentative of actual cellular activities of these hormones.

Attempting to manage the dosage of T3 for someone who can only get well by using T3-Only can only currently be done effectively and safely by using indirect measures of thyroid hormones, as described in my books.

Attempting to do this by using thyroid hormone blood test results could even be dangerous, as all of these thyroid hormone test results may have no bearing on cellular activity. This point is highly relevant for those patients using T3 only and this is a major reason why using T3 is harder than the other hormones. 

Unfortunately, many doctors appear to be unaware of any of this and still cling on to the idea that they can use thyroid blood test results to monitor T3 replacement and manage their patient’s T3 level. This is not only going to fail but it could make the patient very ill.

Someone new to T3 replacement therapy may believe that the medication can be taken in a single daily dose, just like synthetic T4. This may work for a few people but for others, the daily dosage of T3 will need to be split up and taken in smaller doses, known as divided doses. This divided dose approach enables T3 to be taken at various intervals throughout the day, in order to provide a steady supply of T3 to the body.

The use of divided doses also ensures that no single dose of T3 creates an exceptionally high peak level of T3 in the tissues of the body. The majority of patients successfully using T3 use between three and four divided doses of T3 per day.

Using divided doses of T3 clearly adds a lot of complexity to the life of thyroid patients. A further complication of the use of T3-Only is due to the suppressive effect that it can have on TSH. The level of TSH influences the conversion of T4 to T3. A high TSH results in the maximum level of conversion of T4 to T3. A fully suppressed TSH will result in the conversion rate of T4 to T3 being reduced to the minimum level.

For the patient on combined therapy with T4 and T3, this is very significant indeed. Some doctors attempt to perform simple mathematical calculations when they add T3 to their patient’s T4. They reduce their patient’s T4 dosage when T3 is added. Often there is no understanding that the added T3 is likely to have a suppressive effect on TSH and this is likely to downgrade any T4 to T3 conversion rate. So, finding the right balance of T4 and T3 can be an extremely challenging task.

In summary, the use of T3 has a number of difficulties:

  • The half-life of T3 is short and the drug is very potent. T3 usually needs to be taken in three to four divided doses per day. A few patients find that they can cope with only two divided doses.
  • T3 acts quickly and powerfully and will distort thyroid blood test results of TSH, FT4, FT3, and rT3. For someone using T3-Only, these thyroid blood test results are not reliable measures to be employed for managing the treatment.
  • Doctors may wish to try to manage the patient’s T3 dosage using thyroid blood tests and the standard lab ranges – this will not work.
  • T3 used in combination with T4 can also prove difficult. Blood test results can be distorted, divided doses of T3 need to be used and the conversion rate of T4 can deteriorate.

All of the above difficulties mean that using T3-Only is not something that anyone should want to do unless everything else has been tried and failed.

Using T3 in combination with T4 is simpler but has its own issues.

As well as bearing the above in mind, investigations into deficient nutrients or low cortisol levels should be thoroughly performed and ruled out before ever considering the use of T3. T3 is harder to use, so other treatments should be explored first.

I have been known to refer to T3 as the thyroid hormone treatment of last resort – I believe it should be viewed like that.

However, if all the necessary investigations have been performed, and all the thyroid hormone therapies have all been tried and shown to fail, then T3-Only can be a wonderful way of recovering your health. I know – I have done it, and so have thousands of other patients. 

However, a safe and effective protocol needs to be used – this is why I wrote Recovering with T3.

I hope you found this helpful and informative.

Best wishes,


(Updated in May 2021)

Paul Robinson

Paul Robinson is a British author and thyroid patient advocate. The focus of his books and work is on helping patients recover from hypothyroidism. Paul has accumulated a wealth of knowledge on thyroid and adrenal dysfunction and their treatment. His three books cover all of this.

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  1. Gabbe on 12th August 2020 at 7:43 am

    My brother and I had radiation treatment, on our Thymus Gland, as infants. Neither of us convert T4 to T3. My brother had cancer in his Thyroid and had many surgeries to save his life (age 16). I had a tumor on my Thyroid, at age 29. Had surgery to remove my gland. My Dr. turned my surgery over to an intern and he removed the tumor but failed to remove my gland. We have both been under treated ever since. Since TSH has come out life has been hard. I have found a Dr. that gives me T3 and I had been wondering about T3 only but not sure how to go about this. What are your thoughts on this? I would be interested. Also, I wondered if T4 does anything else other than convert to T3.

    • Paul Robinson on 12th August 2020 at 9:45 am

      Hi Gabbe,
      That’s a very sad story. T4 does very little indeed and nothing that the T3 cannot do alone. I wrote my Recovering with T3 book for people like you. I would not decide to use T3 only without reading it. It has enough background information on T3 and a protocol for using T3 only. I would definitely read and digest the Recovering with T3 book before making changes. See my homepage on the website too as I do a few coaching sessions (I won’t do these indefinitely but I still do small numbers of these).
      Best wishes,

  2. Bella on 29th August 2020 at 7:22 pm

    I have had low T4, low T3 and low to middle range of TSH for the last 20 years. I was initially treated with Levothyroxine, then it was stopped as the doctor was going on my TSH results and not my symptoms. After a break of a couple of years where my T4 levels plummeted further I was prescribed Levothyroxine again. I have spent the following 15 plus years still suffering from UAT symptoms. I felt better when my T4 was raised but as this dropped my TSH below range I remained poorly medicated. 3 years ago I switched to NDT and added T3. My endocrinologist wants me to do NDT only but since going down this route I am struggling and find that I am better with adding T3. I have one copy of the DI01 and DI02 genes and have had low cortisol levels for 15 plus years. The Endo also said I either have central hypothyroidism or a pituitary gland that is not functioning properly but as the treatment is the same it was irrelevant which was the cause. 3 years later I am still struggling to find my correct dose of medication.

    • Paul Robinson on 30th August 2020 at 9:43 am

      Hi Bella,
      It does sound like your situation requires a mix of T4 and T3 that suit you. This might mean NDT with T3 or T4/T3. Whichever it is the dosage of the T4 medication might need to be lowered and the T3 increased until your symptoms resolve. Note: TSH level should not restrict this as long as you are not hyper, i.e. a very low TSH is not an issue as it is not an indicator of hyperthyroidism when a patient is on thyroid meds. In addition, if cortisol remains low you might be a candidate for my CT3M protocol to attempt to raise cortisol. It is very common for people with low FT3 levels to have various pituitary issues, as the pituitary needs a lot of T3 to work properly.
      My books cover a lot of this. The Thyroid Patient’s Manual is a great starting place.
      Best wishes,

  3. Eddie Adams on 13th December 2020 at 7:46 pm

    20 years of thyroid replacement. My preferred dose is 40mcgs of t3 and 50mcgs of t4. Can’t take T3 and T4 together. I like half the T3 first thing in the morning, then hours late sneak in the t4, then evening the other half of the T3. T3 is great stuff. T4 is nasty debilitating stuff–but for some reason, I don’t know why, I need some it, otherwise I feel loopy.

    Why this combination? Simple, because I feel better. Nothing more than that. Does it screw up my blood tests? You bet. Do doctors argue with me? You bet. They keep telling me I need twice the T4 and a lot less T3 and every time I try, I get the same result–debilitation. So, I’ll stick with feeling good over lab test results that come back inside the norms.

    Proof is in the puddin, not the lab test result or the book that a Med student reads.

    • Paul Robinson on 14th December 2020 at 10:22 am

      Hi Eddie, thanks for the comment.

      I agree with you. At the end of the day, it is far more important to feel well and have a life than have a set of laboratory test results that please a doctor or endocrinologist. Unfortunately, most of them do not work tirelessly to fix the symptoms of the thyroid patients that they deal with. If a thyroid patient’s lab test results are in range, the doctors feel they have done their job.

      I’m sorry it took you 20 years to get there. It took me 10 to get the thyroid medication solution I needed and then another 5 or so to recover from the damage that the T4 had done.

      Thanks again for your comment! Stay well!

      Best wishes, Paul

  4. joanna on 17th January 2021 at 6:18 am

    i was wondering what is considered to be high t-3? i see some ranges are higher than others. MY tsh is 5.5. which trying to get it lower but my t-3 is 180,
    any suggestions?

    • Paul Robinson on 17th January 2021 at 10:24 am

      It is really hard for me to discuss specific patient situations via this website. I would need a lot more information.

      Labs always vary with the type of assay that they do when they test thyroid hormones. So in some countries and labs an FT3 range might be 3.3 – 6.7 and in others, it can be completely different. So, what is considered to be high will be dependent on the actual lab and the type of assay that they do.

      Also, T3 can be measured as Free T3 (FT3) or Total T3. FT3 is the bioavailable T3 and is much more useful. Usually, the Total T3 is a lot higher with a much higher range.

      Best wishes, Paul

  5. Sharon Fox on 17th June 2022 at 2:15 pm

    My daughter has recently been prescribed T3 (after begging for it- the doctor wasn’t keen. She was diagnosed with Hashimoto’s 13 years ago. At times her blood tests said she was hyperthyroid instead of hypo. She is going to cut her T4 (been on it for 13 years) from 150 to 100 and takes T4 recently in three daily doses. She has also been diagnosed with atrophic thyroiditis. All these diagnoses are confusing and I can’t find sufficient easy-to-understand info on these. Does your book touch on these aspects?

    • Paul Robinson on 17th June 2022 at 2:33 pm

      Hi Sharon,

      1. At times her blood tests said she was hyperthyroid – do you mean that her TSH on thyroid treatment was low? Or that at times FT4 or FT3 were high? With atrophic thyroiditis (AT), you can get variation in the conversion rate of T4 to T3 and at times the TSH signal into the thyroid and other cells is blocked. This makes dosing of T4 meds extremely difficult.

      2. With AT the person is often better off with no T4, or very small amounts T4. So, even 100 mcg of T4 may be too much to cope with. See:https://paulrobinsonthyroid.com/could-atrophic-thyroiditis-be-your-problem-it-is-not-always-about-hashimotos-thyroiditis/

      3. For someone using mostly T3 (which is usually better for AT), I would definitely recommend reading Recovering with T3. T3 use necessitates a different model for dosage management. Blood tests are no longer very much use and signs and symptoms need to be used instead. The book explains this. My The Thyroid Patient’s Manual book is a more general book on thyroid diagnosis and treatment. It also covers all the other tests and elements that ought to be examined and addressed to be sure that the thyroid treatment has the best chance of success.

      Best wishes, Paul

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