What is Reverse T3? And does it matter?

When you are struggling with an underactive thyroid and your symptoms are not getting better, you may have high levels of Reverse T3.  

what is reverse t3

Reverse T3 (also written as rT3) is one of those thyroid tests that most doctors will not request. I believe that many conventional doctors do not understand the value of the test, or they don’t actually know what to do with the results.  It is also an expensive lab test, and some medical aids or medical insurance will not cover it, which means you will have to pay for it out of your own pocket. 

It is also not a test that I will recommend that you routinely check for.  But there is a time and place that it is worthwhile to do the rT3 test.  

What is Reverse T3?

Let’s start with understanding what rT3 is.  

Your thyroid gland produces thyroid hormones which your cells use for metabolism and other metabolic functions.  The thyroid gland produces mostly T4 hormones, which are inactive, and a few T3 hormones, which are the active hormones that your cells can use.

These inactive T4 hormones must be converted to the active T3 hormones.   The cells can then use these active T3 hormones.

Sometimes, it may happen that the T4 hormones are NOT converted to the active T3 hormones, but instead to another version of T3 hormones, namely, Reverse T3 (rT3).  

There are 2 problems with Reverse T3:

  1. The first is that these rT3 hormones are completely useless.  Your body cannot use them for anything.
  2. Second, these rT3 hormones attach to the cells (to the cell receptors) and block the cell from using the active T3 hormones.  

You can start to show symptoms of hypothyroidism or find that your hypothyroid symptoms worsen.  

What causes Reverse T3?

Reverse T3 levels can increase during times of major trauma, surgery (such as a bone marrow transplant), inflammation (4), extreme dieting or starvation, or when you have a severe chronic illness such as HIV or kidney disease. 

I have found that my rT3 increased when I was under a huge amount of work stress and pressure, and my Hashimoto’s symptoms increased!  My body just wasn’t coping with the demands that I placed on it.

It seems that whenever you place your body under severe stress (for whatever reason), you could unknowingly cause an increase in rT3. 

Symptoms of high Reverse T3

You may be experiencing any one or more of these symptoms when your rT3 levels are high:

  • Slower than normal metabolism
  • Picking up weight when you haven’t changed your eating habits
  • Severe fatigue
  • Any of the symptoms of hypothyroidism
  • Chronic pain
  • Feelings of depression and/or anxiety.

Should you test for Reverse T3? And when?

I will not recommend that you do the rT3 test as part of your standard thyroid panel testing.  

This test is expensive, and many medical aids or medical insurance will not cover the cost for it, or will only cover a portion of the cost.  Some medical insurance companies may even require motivation from your doctor before doing the test.  So be aware that you may have to pay for this test, or a portion thereof, out of your own pocket.

That said, I believe there is value in doing this test.  One of the biggest reasons is when your thyroid medications have been optimized, you may have a sudden worsening of hypothyroid symptoms, or you may even have a sudden onset of hyperthyroid (overactive thyroid) symptoms!  

Here is the value of doing this test:

When you have high levels of rT3, I believe the last thing you should do is take more levothyroxine (synthetic T4 medication).  Here is why. 

Remember that rT3 blocks the cells from using T3 hormones?  As rT3 is created by the conversion process from the inactive T4 hormones, if you take more T4 hormones, you may actually increase even more rT3 hormones!  Which then blocks more cells from using the active T3 hormones.  

So, I do recommend that you speak with your doctor about doing the Reverse T3 test when you have major hypothyroid symptoms and you have been under major stress or have a chronic disease.  Especially when you have the autoimmune thyroid disease Hashimoto’s and you really need to know what is going on in your body.

The optimal range

So you tested rT3.  How do you know what the range is what it should be in?

Remember, there is a certain amount of conversion from T4 to T3 that is completely normal.  We want to know when it becomes too high.

According to Dr. Datis Kharrazian in his book “Why do I still have thyroid symptoms when my lab tests are normal“, the optimal functional medicine range for rT3 is between 90 – 350 pg/ml. 

Understanding the lab results

Without becoming too mathematical, you want to have a look at the relationship between T3 and rT3.  The higher the T3 and the lower the rT3, the better!  

There is a simple formula that you can use: take your T3 number and divide it by the rT3 number.  The answer should be bigger than 0.2 (so, anything between 0.2 and 1, and the closer to 1, the better!).

When the levels are too high

If you have high rT3 levels, there are a few things you can do:

Check what is happening in your life.

You should have a look at what is happening in your life and your health.  Are you under severe stress?  Have you experienced trauma?  Do you have an underlying chronic illness that you need to treat?  

Take pure T3 medication.

Consult with your doctor to take a pure T3 medication.  This way you are giving your body T3 hormones directly, without depending on the T4 to T3 conversion to happen. 

Keep in mind when you take T3 hormones, your T4 levels will typically be lower, and your TSH may drop or even become depressed (close to 0). 

Don’t forget to find the reason why your rT3 is high in the first place.  

Supplement with selenium and zinc.

Selenium plays an important role in the conversion of T4 to T3.  Numerous studies have also shown that selenium can help to decrease rT3 production!

Studies have also shown that zinc helps with converting T4 to T3 hormones. 

Reduce inflammation

Reducing chronic inflammation is a complex topic, and you need to find the cause of your inflammation, whether it is food sensitivities, an autoimmune condition, gut imbalance, hormone imbalance, stress, or chronic health condition.  

There are  a few supplements that may be helpful in helping to reduce inflammation:

  • Omega 3 oil
  • Curcumin
  • Quercetin
  • Bromelain

Final thoughts

While many doctors do not believe in the value of rT3 testing, I believe there is a time and place to have it checked.  If you have been experiencing extreme stress or trauma, your body may be converting the T4 hormones to the useless rT3 hormones.  It can be the underlying cause of many persistent symptoms, including that very frustrating weight gain or inability to lose weight when you have hypothyroidism or the autoimmune disease Hashimoto’s.  

Once you know what you are dealing with, you can take action.  


  1. What is Reverse T3? Basile L.M.  Endocrine Web.  Published online 28 June 2021.  https://www.endocrineweb.com/conditions/thyroid/what-reverse-t3.  Accessed 3 June 2022.
  2. Why do I still have thyroid symptoms when my labs are normal.  Dr D Kharrazian, 2010.  Morgan James Publishing.  Pg 99, 248.
  3. Reverse T3 Treatment Guide + How to “Flush” it out of Your Body & Start Feeling Better. Dr Westin Childs.  Published online 25 March 2021.  https://www.restartmed.com/reverse-t3/.  Accessed 3 June 2022.
  4. Interaction of the endocrine system with inflammation: a function of energy and volume regulation. Straub R.H. NIH, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978663/.  Accessed 3 June 2022.
Adele du Rand

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