T3 (Liothyronine) Only Treatment – How to Use Symptoms & Signs, Instead of Thyroid Blood Tests

Thyroid Patient’s on T3-Only Thyroid Treatment, or Mainly T3, Should Not Try to Use Thyroid Blood Tests to Try to Check If their Dosage of T3 is Correct

I am quite doubtful about the value of thyroid blood tests for the dosage management of T4/T3 for some people once the T3 component is more than a very small amount. However, as patients increase T3 and decrease T4, the usefulness of thyroid blood tests to determine if the replacement is adequate begins to decline.

I have to say once again for completeness that thyroid blood tests usually have a very valuable role in the diagnosis of hypothyroidism.

My typical thyroid blood test results back in 2012 looked like this (on my 60 micrograms or so of T3 per day – which is quite a modest amount compared to some patients):

  • TSH is often near zero (but if I leave a gap of 18 hours or more between my last T3 dose and the blood draw, I can make TSH higher).
  • FT4 was 0.3 pmol/L (reference range 12.0–22 pmol/L).
  • FT3 was 8.9 nmol/L (reference range 3.1–6.8 nmol/L).

My thyroid is dead now, having had Hashimoto’s for around 30 years,and I take no T4 medication, hence my FT4 is near zero. I use T3-Only, hence the high FT3.

Most patients on T3-Only have:

  • High FT3 (at or over the top of the reference range).
  • Low FT4 (often below the bottom of the reference range due to suppressed TSH).
  • A suppressed or very low TSH.

Often patients on T3-Only are in a long-running battle with their doctor or endocrinologist to reduce their T3 dose because of high FT3 (which often makes them feel worse), or to add some T4 (which often makes them feel worse also).

I have a once a year thyroid blood test, as my doctor has to do that to conform to admin rules. We ignore the results or at least do not act on them. Some doctors might assume I was thyrotoxic given my FT3 level, but I am not remotely thyrotoxic.

Thyroid blood tests are at best a rough guide as to whether our cells are getting the thyroid hormones that they need. They are an accurate estimate of blood levels but can be desperately inaccurate in terms of cellular levels of thyroid hormones.

In particular, thyroid blood test results usually do not reflect how well or unwell the thyroid patient actually feels. Attempting to use thyroid labs is likely to result in the thyroid patient remaining hypothyroid.

Only the active cellular levels of thyroid hormones count, and we cannot measure this with any laboratory test yet. Am I getting boring yet? I hope so.

There are Ways To Assess the Effect of the Biologically Active T3 Thyroid Hormone Within Our Cells

Many years ago doctors would have used a complicated apparatus to measure basal metabolic rate. In fact, this BMR measurement used to be the only diagnostic method for detecting hypothyroidism. The BMR used to measure the energy consumed by the body when completely at rest. If a patient had hypothyroidism then their basal metabolic rate would have been very low.

A ‘modern’ equivalent of the old BMR machine is called an indirect calorimeter. Indirect calorimetry measures resting metabolic rate, or the number of calories your body burns at rest.  It can also measure how many calories your body burns after eating – but this is a more complex test. The test involves measuring the amount of oxygen a patient breathes in, and the amount of carbon dioxide breathed out.  From this data, the number of calories burned per minute is determined.  The patient has to lie down and wear a special clear canopy over their head and neck. The canopy is ventilated, lightweight and comfortable. Patients have to fast for 10-12 hours prior to a resting metabolic rate test, and lie quietly for the 45 minutes duration of the test. The patient needs to avoid going to sleep and just lie quietly for the 45 minutes of the test (watching TV is fine).

However, few doctors use indirect calorimeters and most patients have to rely on cruder methods to provide data on how well thyroid hormone is regulating cell function.

Symptoms and Signs are Indicators of Cellular Levels of Thyroid Hormones

So, we have not got a laboratory test that indicates how well thyroid hormone is actually regulating our cells. Most of us haven’t got access to and can’t afford an indirect calorimeter. So, what can we do?

All we can do is measure the effect of these thyroid hormones on our body. This is what I have done for well over twenty years. I use symptoms and signs.

A doctor describes a sign as something that is objective and can be measured. A symptom is a subjective assessment of something.

So, a patient may say, “I feel cold”. Feeling cold is the symptom and body temperature is the sign.

Anyone who suspects that they are still hypothyroid can track symptoms and signs every day and build up a diary record of these, which can be used to determine if they are hypothyroid at the cellular level. A doctor who is not open-minded may not accept this. Many doctors may not be convinced.

However, for someone on T3-Only – this is currently the ONLY reliable method, to manage the T3 divided doses, until some researcher comes up with a proper test of thyroid hormones that shows how well thyroid hormone is actively regulating cell function.

Anyone on T3-Only who has a doctor who is attempting to manage their T3 dosage entirely with thyroid blood tests (TSH, FT4, FT3), ought to or attempt to explain that this isn’t possible. It will result in very BAD decisions being made that could easily keep the thyroid patient HYPOTHYROID.

If this does not work they should change doctor. This may also be true of people who take predominantly T3 with some T4. 

Here is the list of symptoms and signs that I use on a regular basis:


  • Mood. 
  • Anxiety (including restlessness, hyperactivity or irritability, being anxious, edgy, tense and unable to relax, usually means too much thyroid hormone).
  • Mental ability and clarity.
  • Energy level.
  • Muscle weakness.
  • Digestive system performance.
  • Condition of skin, hair and nails.
  • Heat or cold sensitivity.
  • Muscle aches or pains.


  • Resting heart rate.
  • Blood pressure.
  • Body temperature.
  • Weight gain/loss.

I have been brief with the list of symptoms and signs, and not explained fully how I use them, but the list should give a pretty good indication that dosage management with T3 is not as simple as T4, but it is possible to do it well.

It is also important to use symptoms and signs to determine when each T3 dose is due during the day – taking a T3 divided dose too early is just as bad as taking too much. The Recovering with T3 book has a T3 dosage management process, which is designed to determine only the amount of T3 that is needed to regain good health and no more than this. 

Until thyroid researchers develop new laboratory tests of how well thyroid hormone is regulating the function of our cells, the use of symptoms and signs is the only reliable way of managing the dosage of T3 only replacement.

The Recovering with T3 book emphasises safety and caution. The T3 dosage management process that is described in detail within the book, allows the patient’s T3 dosage to be determined safely and effectively. I continue to hope that over time some of the more open-minded doctors and endocrinologists will read it and find some value in it also.

Best wishes,


(Updated in March 2020)

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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