Hashimoto's Thyroiditis is an autoimmune condition in which the immune system produces antibodies that attack the thyroid gland, the butterfly-shaped gland in the neck responsible for producing hormones that regulate metabolism, energy, mood, temperature, digestion, and virtually every other system in the body. Over time this immune attack progressively damages thyroid tissue, reducing its ability to produce adequate hormones and resulting in hypothyroidism. Hashimoto's is not primarily a thyroid problem. It is an immune problem that happens to target the thyroid. Treating the thyroid with hormone replacement without addressing the immune attack driving the damage is why so many people on thyroid medication continue to feel unwell.