Science shows that 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, meaning a healthy thyroid doesn’t force you to get it from conversion alone.

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, as experienced and reported by patients over the years?

STTM graphic common reasons for RT3

Summary: issues which commonly cause rising levels of reverse T3 include high cortisol, low cortisol, low iron, lyme disease,chronic inflammation, or other chronic health issues.

***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.

Are there other reasons I could have too much RT3, even though the above are the main reasons for thyroid patients??

Yes, they include:

  • Beta-blocker long-term use such as propranolol, metoprolol, etc.  See this study.
  • Chronic inflammation, whatever the cause, has risen RT3 in patients.
  • Physical injury, a common cause of increased RT3
  • Illnesses like the flu, a common cause of increased RT3
  • Starvation/severe calorie restriction is known to raise RT3. See this study.
  • Diabetes when poorly treated is known to increase RT3. See this study.
  • Lyme disease

Not necessarily related:

Lithium is sometimes stated to increase RT3, but for most, it hasn’t. Lithium instead inhibits the release of thyroid hormones from one’s thyroid due to the blocking against iodine, and instead, can lower RT3.

Excessively low carb diets are sometimes stated to increase RT3, but studies don’t show this. Instead, it may be more about calorie restriction.2

What are symptoms that I have an RT3 problem?

Since Reverse T3 is an inactive hormone, and since this hormone in excess will bind to your thyroid receptors and start to prevent T3 from getting to your cells…the symptoms are increased hypothyroidism! i.e. whatever are your particular symptoms of being hypo will increase. It’s individual. This could include more fatigue, for example, or an increase in adrenaline creating anxiety, or increased depression, or an increased need to nap…on and on. Or a rising RT3 can mean that no matter what you have done, you still have irritating hypothyroid symptoms!

Can lab work 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 Free T3/RT3 or the Total T3/RT3.
 i.e dividing the Free T3 by the Reverse T3 (Free T3 ÷ RT3) or dividing the Total T3 by the RT3 (total T3 ÷ RT3)…though they need to be in the same measurement or changed to the same measurement.

Using the FT3/RT3 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 or higher.

For the Total T3 ratio, it should be 10 or less. The Institute of Functional Medicine supports the Total T3/RT3 ratio.

Do work with your doctor on this information.

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

Summary: patients with high RT3 have learned to primarily lower their NDT to 1 1/2 grains or less, since RT3 comes from the T4. Some can add in T3 to that lowered dose, such as 5 mcg and 5 mcg, but it’s important to watch for pooling of that free T3. Supporting the liver has outright helped patients since RT3 is primarily made in the liver, such as using Milk Thistle, Dandelion root or other supplements. Some sources say Selenium at 200 – 400 mcg can help lower RT3, though it can be important to test your selenium levels to make sure they aren’t already too high.


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. Share this information with your doctor.

What if my doctor pooh-poohs this problem with Reverse T3?

Share the following with him or her, i.e. even the pharmaceutical company which makes the injectable form of T3 called Triostat states the following:

The prohormone T4 must be converted to T3 in the body before it can exert biological effects. During periods of illness or stress, this conversion is often inhibited and can be diverted to the inactive reverse T3 (rT3) moiety.

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 at 1.5, 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:
  • 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.”




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