Complex sentence: Potassium perchlorate has, in the past, been used therapeutically to treat hyperthyroidism resulting from Graves' disease via interfering with accumulation of iodide in the thyroid, which results in the blocking of hormone production.
Split into simpler sentences: Potassium perchlorate has, in the past, been used therapeutically to treat hyperthyroidism resulting from Graves' disease. It impedes the accumulation of iodide in the thyroid, which results in the blocking of hormone production.