​Reverse T3 (rT3, reverse triiodothyronine): the hormone of hibernation &/or starvation.
Produced by: Thyroid gland. Controlled by the hypothalamus and pituitary gland (brain).
Purpose: To modulate metabolism by competing with fT3 at its receptor sites.
Definition: Reverse T3 is the opposite of T3. It is an inactive thyroid hormone. It is a mirror image of T3 and goes to the same receptors, sticks there, and blocks T3 from docking into the receptors. So it blocks the thyroid effect. Reverse T3 is sort of a hibernation hormone, in times of stress and chronic illness, it lowers your metabolism. Many people will have normal thyroid lab tests, but if they have high Reverse T3, they will feel like they have hypothyroidism.
Lab Reference Range: 8-25 ng/dL
When to order:
- To initially screen for hyper or hypothyroidism
- To monitor thyroid medication usage.
Pearls:
Half-life: 4 hours.
If RT3 is high – you are likely converting too much T4 to RT3 and not enough to FT3, which can cause hypothyroid symptoms even if your TSH and T4 levels are optimal
Your body uses a portion of the T4 to create Reverse T3 which is an inactive form of thyroid hormone. But even though it is inactive, it can attach itself to the same receptor sights within every cell in your body that Free T3 would normally attach to and block Free T3 from doing its job. Thus lowering metabolism.
When you have an elevated rT3 level, this is also called “Thyroid Resistance”, “Thyroid Pooling” or “T3 Pooling”. Think of it like musical chairs. If you have a high rT3, which team is going to win? rT3 and fT3 compete with each other for the T3 receptors on every cell in your body.
Causes of elevated rT3
  • Being on too high of a dose of a T4 prescription like Synthroid. Your body starts converting it to rT3 to protect you from becoming hyperthyroid.
  • Any situation where your brain thinks you are starving or hibernating. Examples would be if you are fasting or trying to decrease your calorie intake to lose weight. This is why some people can’t lose weight even though they are eating nothing. Their body is compensating by increasing rT3, lowering metabolism and protecting the body from death. Certain medications can increase rT3. For example, the drugs that are used for heartburn or GERD which stop the production of stomach acid. Unfortunately, you need stomach acid to adequately absorb minerals, amino acids, proteins and B Vitamins. Now in this situation, your brain thinks your starving or hibernating and gets your body to make more rT3.
  • Graves’ Disease and hyperthyroidism will have an elevated rT3 because of the high T4 levels. Your body is trying to compensate or equalize the high levels of T4 and T3.
  • Physical or emotional STRESS will cause an increase in rT3.
  • Adrenal fatigue can trigger low stomach acid production and elevated rT3.
  • Low ferritin (a protein that is produced by nearly every cell in your body that stores and transports iron).
  • Any acute illness and injury.
  • Any chronic disease.
  • Old age. Stomach acid production decreases as we age.
Ratios of fT3/rT3 are important. As an example, if your fT3 lab test results come back at 2.9 pg/mL, and your rT3 level comes back at 23 ng/dL, you are technically in the normal range for both hormones. But if you look at the ratio or where each test sits within the normal range, in this situation you have relatively more rT3 than you do fT3.
Free T3 can not convert into reverse T3. Only T4 can make rT3.

Some examples on how to Lower Reverse T3 (After consulting with your doctor)
1. GastrAcid: 1-3 with each meal. Increase to tolerance. If you get heartburn, decrease dose. This supplement increases HCL in your stomach which aids in the absorption of minerals, amino acids, and B Vitamins. Improved absorption means your brain does not think you are hibernating or starving and rT3 will decrease. (DR.T patients use discount code: holysmokes!)
2. Increase your T3 prescription and decrease your T4 prescription (after consulting with your physician)
3. Get enough Sleep. At least eight hours
4. Increase your metabolism through exercise look into ketogenic diets adn intermittent fasting (after consulting your physician)