Reverse T3 is a naturally occurring thyroid hormone byproduct that makes up a significant portion of thyroid hormones in your blood. It's created when your body converts another hormone called T4, and its levels stay steady enough that doctors can easily measure them with current lab tests.

A substance called rT3 blocks your body's active thyroid hormones from working properly by taking their place on cellular receptors. This prevents your cells from getting the energy signals they need, which ultimately slows down your metabolism.

Reverse T3 is a byproduct of your thyroid hormone system that doesn't activate your body's metabolism like normal thyroid hormones do. Instead, it acts like a traffic cop that redirects your thyroid hormones away from becoming active, helping your body control how much thyroid hormone is actually available to use.

This claim suggests that checking a specific thyroid hormone called rT3 in the blood could help doctors better understand mood and thinking problems. Adding this test to regular thyroid checks might lead to more accurate diagnoses and treatments tailored to how a patient's body processes hormones.

Your body uses iodine to build thyroid hormones — without iodine, it can't make the key hormones that help control your metabolism.

A thyroid hormone byproduct called rT3 might block the active thyroid hormone from working properly in your brain cells. This blockage could lower the hormone's effectiveness, which might play a role in causing certain mental health and brain development issues.