Antithyroid drug therapy is currently the most widely used in China. The advantages lie in the dosage adjustment is relatively convenient, low price, the incidence of persistent hypothyroidism after treatment is low; the disadvantage is that the course of treatment is longer, the recurrence rate is high after stopping the drug, and sometimes it can produce more serious side effects of the drug. (1) Drugs: At present, the most used drugs in China are propylthiouracil and methimazole. (2) Pharmacological mechanism of action: at present, it is believed that it is mainly through the inhibition of thyroid peroxidase activity, which plays a role in preventing the synthesis of thyroid hormones. ①Inhibit the combination of iodine and tyrosine in the thyroid gland, i.e., inhibit the formation of monoiodotyrosine and diiodotyrosine. (ii) It prevents the coupling of iodinated tyrosine to T3 or T4. (iii) Propylthiouracil (PTU) also prevents the conversion of T4 to T3 in peripheral tissues. This effect is positively correlated with dose and is more pronounced when the dose is greater than 600 mg/d. ④ This group of drugs also mildly inhibits immunoglobulin production, resulting in fewer lymphocytes in the thyroid gland and a decrease in TRAb in the circulation. (3) In vivo processes and effects: thiourea drugs are absorbed rapidly after oral administration, 20~30min that is, they begin to appear in the blood, and the concentration reaches the peak within 2h; they can be distributed in all tissues of the body, but the concentration in the thyroid gland is the highest. This drug can pass through the placenta, use with caution in pregnancy; the concentration in breast milk is also high, so it is prohibited during lactation; mainly metabolized in the liver, about 60% is destroyed, partially combined with glucuronic acid and excreted; metabolism is faster, the action time is not long. Propylthiouracil (PTU) half-life in vivo is only 90s, methimazole (tabazole) for 6h, but the plasma concentration of the drug and its duration of action, the relationship is not close, because thioureas are in the thyroid gland after the gradual accumulation of the effect. (4) Indications: ① adolescents and children patients; ② mild and moderate hyperthyroidism; ③ pregnant women; ④ recurrence after subtotal thyroidectomy, and is not suitable for radioactive 131I treatment; ⑤ hyperthyroidism with severe protruding eyes, can be treated with a small dose; ⑥ to do the preparations for pre-surgery or radioactive 131I treatment; ⑦ due to the accompaniment of serious organic diseases, such as severe heart disease, bleeding disorders, and those who can not be operated. (5) Dosage and course of treatment: the total course of thiourea treatment is at least 2 years, which can be roughly divided into 3 stages. ① Primary treatment stage: the primary dose needs to be determined according to the condition. For patients with severe symptoms or obvious goiter, the dose should be higher; for patients with milder symptoms, extremely high titers of TGAb and TMAb, obvious proptosis and combined pregnancy, the dose should be lower. Generally speaking, for patients with different degrees, methimazole (thiamazole, tapazole, tabazole) 20~60mg/d; PTU 200~600mg/d is more appropriate, both divided into 3~4 times. The initial treatment stage is usually 1~3 months, symptoms often begin to ease in 2~3 weeks, if the drug 3 months of symptoms still do not improve, should consider increasing the dose, and check whether there are interfering factors, such as irregularity of the medication, as well as taking iodine, infections, and other stressful situations. Most patients after 3 months of treatment, hyperphagia, excessive sweating, irritability and other symptoms improved significantly, weight gain, but whether to enter the dose reduction stage still need to be determined on a case-by-case basis, the following conditions can be used for reference; the above symptoms improved significantly, the thyroid gland began to shrink, the neck and precordial murmur weakened; FT4, TT4 and T3 have fallen to the critical range; in the case of discontinuation of β-blockers, the heart rate is stable in the quiet lying at 80 beats/s. ② Reduction stage: after meeting the above conditions and entering the reduction stage, the drug dose can be reduced by 1/3, observed for 2~4 weeks after the reduction, and then reduced by 1/3 if the condition is stabilized, and closely observed. The dosage should not be reduced too rapidly, and when the symptoms rebound, the dosage should be increased appropriately and stabilized for 2~4 weeks. After 1~3 months of dose reduction, if the condition is still stable, then enter the maintenance phase, the following conditions can be used for reference; symptoms and signs of hyperthyroidism basically return to normal and stabilize for at least 2 weeks; FT4, TT4, and T3 are in the normal range; ultrasensitive TSH rises to the normal range; in the case of discontinuing β-blockers, the heart rate can be stabilized at less than 85 beats/s in daily life. (iii) Maintenance phase: the size of the maintenance dose needs to be determined on an individual basis, and each patient can explore a dose that suits him or her. Patients can follow the method of the reduction phase to reduce the dose of medication, when reduced to a certain dose can not be reduced (otherwise the symptoms rebound), that is, the patient’s maintenance dose. It has been proved that the maintenance dose for most patients is 2.5~10mg/d of methimazole (tabazole) and 25~100mg/d of PTU. The maintenance phase should last at least 1 year. Discontinuation: Generally, discontinuation of the drug should be considered after 2 years of use, and the following conditions must be met when discontinuing the drug; disappearance of various symptoms and signs, and stabilization of the disease for at least 1 year; FT4, TT4, T3, and ultrasensitive TSH and other indexes have returned to normal for at least 1 year; at least two consecutive negative TRAb tests, with an interval between the two tests of 3-6 months; the usual maintenance dose of methimazole (tabazole) <5mg/d, PTU 25-100mg/d. The maintenance stage should be for at least 1 year. 5mg/d, PTU<50mg/d. Thyroid hormone levels should be rechecked every 2~3 months throughout the medication process, which can be used to determine the efficacy of the treatment, but also used to prevent drug-induced hypothyroidism caused by overdose of thioureas; the dosage should be reduced in a timely manner in the event of hypothyroidism. After the above systematic treatment, most patients can recover, but for patients with various complications and more serious conditions, must be based on the specific conditions of comprehensive treatment, the clinical experience of the physician is very important. (6) Drug side effects: the most common side effects of anti-thyroid drugs are rash, liver damage, granulocytopenia or deficiency, in which granulocyte deficiency is the most easy to miss the diagnosis, which is very harmful. ①Toxic side effects of thioureas on granulocytes: the incidence of this side effect is low, but the consequences are serious. A. Granulocyte deficiency: the absolute number of neutrophils is <0.5×109/L. It occurs 4~16 weeks after taking the drug, the condition is dangerous and the prognosis is poor, therefore, the count and classification of white blood cells must be followed up regularly during the period of taking the drug, once or twice a week at the stage of the initial treatment, and once every 2 weeks after 3 months, and the patient is instructed to follow up the consultation if there are symptoms such as fever, sore throat, and muscular pains, etc., during the period of taking the drug. Once the diagnosis of granulocyte deficiency is confirmed, close sterilization and isolation should be given immediately, and treatment with antibiotics, pro-granulocyte generating drugs, glucocorticoids and so on. Thiourea drugs should be prohibited after recovery. B. Granulocytopenia: more common. It refers to the number of white blood cells <3.5×109/L, or neutrophils <1.5×109/L. Because many patients with hyperthyroidism have low granulocytes, the granulocytes can be further reduced after treatment with thioureas, and the blood should be monitored closely, and the dose of the drug can be reduced or switched to another preparation if necessary. In most cases, the decrease in granulocytes is only temporary and can be restored later; in a few patients, the decrease will continue. Generally, if the white blood cell count is <3.0×109/L or the neutrophil count is <1.5×109/L, the drug should be stopped for observation and necessary measures should be taken. After the granulocytes rebound, try to avoid using thioureas again. ② Rash: some patients may develop various different types of rashes in the initial treatment stage, most of which are mild. In general, it is not necessary to stop the drug, and can be taken with antihistamines. If there is more serious exfoliative dermatitis, the drug must be stopped and glucocorticoid therapy must be used early. ③ Other toxic reactions of the drug: less common, including arthritis, myalgia, neuritis, vertigo, thrombocytopenia, cholestatic hepatitis, alopecia, hair pigmentation abnormalities, loss of taste, enlarged lymph nodes and salivary glands, edema, nodular polyarteritis, lupus erythematosus-like syndrome, toxic psychosis and so on.