There are two types of antithyroid drugs, one is imidazole, often used as methimazole, and one is pyrimidine, namely propylthiouracil. The most common side effects of these two drugs after patients use them are: 1) liver function damage; 2) blood routine, suggesting a decrease in white blood cells or granulocytes, both of which are very common. Therefore, it is important to review the nail function and blood routine regularly during the treatment of hyperthyroidism. There are also some rare side effects, for example, some people have metamorphic reactions, such as skin rash, itchy skin, hives, and a few have vasculitis and muscle aches after taking it. But these are rare. The most common ones are liver function and blood routine abnormalities, and serious liver necrosis can occur. Therefore, it is safe for patients to take hyperthyroidism medication and to have their liver function and blood count checked regularly for one or two months.