In people with Hashimoto thyroiditis, taking thyroid hormone medication often does not eliminate ongoing symptoms even when blood tests show thyroid hormone levels are normal, suggesting that immune system activity unrelated to hormone levels may also be involved in causing those symptoms.

Even when thyroid hormone levels are fixed with medicine, some Hashimoto’s patients still feel sick because their immune system is still attacking the thyroid. This study shows that when doctors use a drug to calm the immune system, symptoms improve—even without hormone pills—proving the immune system itself is part of the problem.