"A normal thyroid gland produces about 80 percent T4 and 20 percent T3. However, T3 possesses about four times the hormonal strength. Both hormones are then secreted into the blood, causing the levels of TSH to fall. In this way, the thyroid gland is like a furnace and the pituitary gland is like a thermostat. The levels of TSH and T3/T4 are always in balance."