Our Thyroid gland produces several hormones that are often overlooked. Most Primary Care doctors (and even many Endocrinologists) who do not check TOTAL Thyroid function. They look only at one hormone called Thyroid Stimulating Hormone (or TSH) which is made by the Pituitary gland in the Brain. If the Thyroid is producing too little of its Thyroxine hormone (or T4), the Pituitary will secrete more TSH to stimulate the Thyroid to increase its production. TSH and T4 have, therefore, an inverse relationship. When one is up, the other is down. When everything's in balance they are both "in the normal range". The problem is not everyone's normal range is the same even though lab tests would have us believe they are. And, further, there is a third hormone to be considered. Triiodothyronine (or T3) is what the T4 produced by the Thyroid becomes once it enters the body's circulation. Each T4 molecule needs three available iodine molecules to transform itself into T3 which is the hormone our tissues need. T4 is weak in its action. T3 is strong - if the body can make it. You can readily see that simply testing the TSH of someone complaining of fatigue is incomplete. It usually results in a Patient being told that their Thyroid is within "normal" range and not part of why they feel so unenthusiastic about their lives.
Addressing the Thyroid has helped many of my patients to feel like themselves again.