This is a contentious issue among thyroid experts: Some say that T4-to-T3 conversion can be impaired and that T3 supplementation is necessary to fully correct thyroid status. Others argue that T3 is unnecessary. There are studies supporting both sides of the argument, with some studies showing improved mood and energy with T3 added to T4, while others fail to show any improvement.
My experience has been most consistent with the first side of the argument: When someone responds "No" to my question about whether they feel normal, I will ask them to consider adding T3 thyroid hormone to their T4. (This is done by either adding a T3 preparation, liothyronine or Cytomel, or by switching to combination preparations like Armour thyroid or Naturethroid.) With rare exceptions, within a week they feel energized, mood improves, excess weight starts to drop
The cognitive side effects of my cancer, however, make me feel old before my time and have tanked my self-esteem....I've turned to my doctors for validation. But, like dozens of thyroid cancer patients I've spoken with about memory loss, my doctors do not acknowledge my symptoms, much less explain the causes.