A healthy thyroid produces the focogsllowing hormones: T4, T3, T2, T1 and calcitonin.  T4, a storage hormone and the most abundant, is meant to convert to T3, the active hormone.  T3 is also made directly.

But there’s another substance produced by the thyroid called RT3, which stands for Reverse T3, and it comes from the conversion of the storage hormone T4. And it’s normal to have RT3. (1)

Why does anyone produce RT3 (Reverse T3)?

Your body, especially the liver, can constantly be converting T4 to RT3 as a way to get rid of any unneeded T4. In any given day, it’s stated that 40% of T4 goes to T3 and 20% of T4 goes to Reverse T3.

But in any situation where your body needs to conserve energy and focus on something else, it will change the above percentages, changing the conversion of RT3 to 50% or more, and the T3 goes down, down. Examples are emotional, physical, or biological stress, such as being chronically or acutely sick (the flu, pneumonia, etc), after surgery, after a car accident or any acute injury, chronic stress causing high cortisol, being exposed to an extremely cold environment, diabetes, aging, or even being on drugs like beta blockers and amiodarone. But there’s another reason for thyroid patients. Read on.

What specifically are the reasons I, as a thyroid patient, make “too much” RT3?

STTM graphic common reasons for RT3

***Note that you can have either an iron problem, or a cortisol problem, or BOTH. There are other reasons you have high RT3, such as the excess inflammation and more, but the above are quite common and worthy to explore first.

Can labwork help me discover this? What do I look for?

First, thyroid patients feels there’s room to be suspicious when the Free t4 is higher in the range for awhile, especially above 1.4 if using the ranges where the top of the range is 1.7. Some notice it when their free T3 goes lower (i.e. the more RT3 you have, the less T3 you will have from conversion). Even having a high Free T3 due to adrenal or iron problems (see below) can be the beginning of also acquiring too much RT3.

Doing the RT3 lab test has given patients the best clue.

With the RT3 lab result, patients and their doctors look for two clues:
1) The RT3 result by itself is 11 or higher. We have seen that correspond with rising RT3.
2) The ratio between the RT3 and the Free T3.
 i.e dividing the Free T3 by the Reverse T3 (Free T3 ÷ RT3)…though they need to be in the same measurement. See the I hate math heading below.  Using the ratio, and for healthy amounts of RT3, the ratio result should be 20 or larger according to Dr. Kent Holtorf (info below). If lower, you may have a problem. Janie has noted that many patients without an excess RT3 issue have a result of 23 or 24.

If you use the total T3, patients are looking for a ratio greater than 10. If lower, it appears to be a problem.  Note that the unit of measurements for the RT3 and Free T3 are often different on your lab results and will need to be changed in order to be the same. Figuring out your ratio is here.

Can I order my own labwork for this, since I doubt my doctor will do this?

To order your own labwork, go here.  It’s legal. Remember to order a free T3 with the RT3 at the same time for ratio comparison, as well.

I hate math. How can I figure out my ratio?

If you don’t feel very math-savvy, STTM has created a beta conversion method for you, here. It still has a few kinks in places we are trying to work out. So let Janie know if you discover one.

How do I treat excess RT3?

STTM graphic how patients lower high RT3



a) Sources say Milk Thistle needs to come from the seeds. Milk Thistle not from the seeds can have an estrogenic effect. Some patients use two more more supplements to improve liver and lower RT3.

b) If on synthetic T4 and synthetic T3 with high RT3, patients are known to scrap the T4 for awhile.

c) See the Odds and Ends chapter in the revised STTM book for more about iron

How do I dose T3 if I choose to use that to lower my RT3?

Excellent patient information is found here. 

Is this RT3 info in the Revised STTM book?

Yes, you’ll find good info about the Reverse T3 in the T3 chapter which can be taken into your doctor’s office and referred to, as needed, as you work to teach your doctor about its use.

Can I make too much RT3 simply from over-dosing my natural desiccated thyroid?

Definitely, I, Janie, accidentally had that happen when I moved from 3 1/2 grains to 4 grains one year recently, thinking an issue I was having meant I needed more thyroid. It didn’t. So my body had too much FT4, and it converted to higher and higher levels of RT3 to clear it out.


  • Have more good research studies for this RT3 page? Send them to STTM via the Contact link below.
  • Where can I talk to others about this?? Go here.
  • See an updated blog post about RT3: http://www.stopthethyroidmadness.com/2009/11/18/reverse-t3/
  • Read what Dr. Holtorf says about RT3 here.  If you scroll down on the page, you’ll also see mention of a study done with elderly men and RT3.
  • Additionally, in the study article titled “Reverse T3 is the best measurement of thyroid tissue levels” found in the 2005, volume 90 issue of The Journal of Clinical Endocrinology & Metabolism, it states that  “the T3/rT3 ratio is the most useful marker for tissue hypothyroidism and as a marker of diminished cel­lular functioning.”

(1) http://press.endocrine.org/doi/abs/10.1210/jcem-41-6-1043


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