Reverse T3 is a thyroid molecule that is similar to regular T3, except one of the iodine atoms is in a different position. This makes it inactive. T3 is the active hormone that the body uses.
High reverse T3 (rT3) levels or a “bad” reverse T3 ratio (Free T3 divided by rT3 is less than 20) are said to be the cause of stubborn hypothyroid symptoms even when someone is taking an ample amount of medication. If the ratio is less than 20, then the treatment touted by some is to take 75-125 mcg of T3 only split throughout the day, and no T4 whatsoever. Some people can tolerate these high doses of T3, others cannot.
Why do so many experience side effects on the T3-only protocol? The reasons are explained in the posts within this category, but here is a quick summary, which basically proves that the reverse T3 ratio theory is based on faulty premises. Recent research in cellular and molecular biology shows that:
- rT3 does not block the receptor at all; neither rT3 nor T3 is in the receptor, that’s the problem
- T4 is more than a prohormone and is essential for healthy hair, brain, and other functions
- Excess T3 will cause an imbalance in other hormones (it raises estradiol, which can be problematic, especially for men)
- Excess T3 (desiccated thyroid has a high amount of T3) can trigger high reverse T3
- Desiccated thyroid contains rT3, because rT3 is found in a normal thyroid gland [desiccated thyroid contains T4, T3, rT3, but little T2 or T1]
- The reverse T3 ratio is a nonsensical number because the ratio can be low when Free T3 is high or Free T3 is low. A high FT3 and a low FT3 are different conditions and should not be treated the same way.