Resistance to thyroid hormone is a rare condition where the body's tissues do not respond properly to the thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3). This can lead to symptoms similar to those of hypothyroidism, such as fatigue, weight gain, and sensitivity to cold, despite normal or elevated levels of thyroid hormones in the blood. The condition is often caused by genetic mutations affecting the thyroid hormone receptor, which is responsible for mediating the effects of these hormones in the body. Diagnosis typically involves blood tests and clinical evaluation, and treatment may include higher doses of thyroid hormone to overcome the resistance.