evidence: Usually in Hashimoto's disease, the immune system produces an antibody to thyroid peroxidase (TPO), a protein that plays an important part in thyroid hormone production. Most people with Hashimoto's disease will have thyroid peroxidase (TPO) antibodies in their blood. Lab tests for other antibodies associated with Hashimoto's disease may need to be done. Most people with Hashimoto's disease take medication to treat hypothyroidism. If you have mild hypothyroidism, you may have no treatment but get regular TSH tests to monitor thyroid hormone levels. [...] Hypothyroidism associated with Hashimoto's disease is treated with a synthetic hormone called levothyroxine (Levoxyl, Synthroid, others). The synthetic hormone works like the T-4 hormone naturally produced by the thyroid.