What is T3?
T3 is an important hormone that is produced by the thyroid gland. Together with the other hormones produced by the thyroid (T4, rT3, and calcitonin), T3 is crucial for processes including metabolism, heart rate, growth, and development.

What Does T3 Do?
When the thyroid gland releases T3 hormone, it causes a general increase in cell metabolism. It also leads to:

• Increased heart rate and blood volume
• Heat production
• Extra oxygen delivery to the tissues
• The promotion of skeletal development
• Increase in wakefulness and alertness
• The regulation of reproductive hormones in men and women
• Increased gastrointestinal function
• Regulation of pituitary function

Forms of T3 in the Body:

• Free T3: Circulates freely in the body and isn’t attached to anything.
• Bound T3: Bound to a protein and does not directly affect bodily processes.

Only the free form of T3 affects bodily processes.