For most people, giving only T4 is good enough because they can easily convert the much less active T4 to the much more active and effective T3. Some people have low T3 levels in their cells (called free T3) despite having normal levels of T4 and TSH. So T4 alone is effective (if the dose is correct, and it often isn't) in about 85% of patients. Therefore, about 15% of people have a genetic problem converting T4 to T3. This means over 1 million people in the U.S. still feel and are hypothyroid even with normal TSH and T4. They need T3 given to them to be normal. Obviously, if you test more thoroughly, you see that not all hypothyroid patients are the same.
Another way mainstream practitioners fail to identify those who need T3 is by not measuring anti-thyroid antibodies which can be a reason for slowing thyroid function. They were taught this. Integrative medicine and functional medicine practitioners usually test more thoroughly to find out why so many people come to us, desperate to find out why they are still tired and overweight. Gluten sensitivity testing (not the blood test for celiac disease!) should be done too because gluten can stimulate the production of anti-thyroid antibodies which in turn slow down the thyroid function.
Take home summary:
1. Most people do well on synthetic T4 (levothyroxine) alone. Even many of those are under-dosed.
2. Approximately 15% don't do well because testing and dosing have been incomplete.
3. Mainstream doctors need to listen more carefully and empathetically to their patients.
4. Have someone test the following before making a final decision on which thyroid hormones and doses are really needed to feel optimal:
Free T3 (free means bioactive, in the cells)