When you start taking levothyroxine or other T4 med, your TSH (thyroid stimulating hormone) goes down, resulting in less stimulation of the
thyroid gland and less output of natural
thyroid hormone. The net effect is basically no change in your important thyroid levels: Free T4 and Free T3, until your med dosage is adequate to essentially suppress TSH level. Then further increases in dosage allow your your Free T4 and Free T3 levels to rise as needed to relieve symptoms.