The iodine organification in thyroid gland was inhibited by application of Thyrostatic (Methimazole, Carbimazole) and consequently, thyroid hormone production and excretion were diminished. Carbimazole is converted to Methimazole in vivo and in vitro. Equivalent doses of Carbimazole and Methimazole are 0.6 to 1.0. Methimazole penetrates through the placenta, therefore established therapy with Methimazole (or Carbimazole) and thyroid hormone are contradicted in states of gravidity. In hyperthyroidism, preferred therapy strategy is accepted as Methimazole and/or Carbimazole only and in low doses, respectively (40-60 mg Methimazole as first step, consequently to doses down to 5-10 mg daily); accompaning rates of hematopoetic damage are dose responded.