Take propylthiouracil for about 1 month to see the effect. Propylthiouracil is an antithyroid drug that inhibits the thyroid’s uptake of iodine and reduces the conversion of T4 to T3, thus inhibiting the synthesis of thyroid hormones and effectively treating hyperthyroidism. However, propylthiouracil can only inhibit newly synthesized thyroid hormones, and the half-life of synthesized thyroid hormones is two to three weeks. After taking propylthiouracil, the synthesized thyroid hormones need to be completely metabolized in the body before it can inhibit the synthesis of thyroid hormones. It takes one month to effectively stop the synthesis of thyroid hormones, so it usually takes about one to two months for propylthiouracil to be effective. Patients with hyperthyroidism should go to the hospital and take anti-thyroid hormone synthesizing drugs as prescribed by the doctor for appropriate treatment.