Hypothyroidism, short for hypothyroidism, is a common endocrine disorder that occurs when the thyroid tissue fails to secrete sufficient amounts of thyroid hormones to meet the needs of normal body function due to a variety of causes. The most common causes of hypothyroidism in adults are Hashimoto’s thyroiditis, hyperthyroidism or thyroid cancer after radioactive 131I treatment or surgery, subacute thyroiditis, and drug-induced hypothyroidism. In children, the most common cause is congenital hypothyroidism (also known as cretinism) due to iodine deficiency. The main symptoms of hypothyroidism are: weakness, fatigue, sleepiness, decreased sweating in those who used to sweat, dry, rough skin, fear of cold, dry, thinning hair, lack of energy at work, lack of concentration, memory loss, mental retardation, poor appetite, bloating, constipation, weight gain, slowed heart rate, decreased sexual desire, impotence in men, excessive menstruation and prolonged menstruation in women. Patients always feel that their face, hands and legs are swollen, but there is no indentation when they press with their hands, and in severe cases, pericardial effusion and mucinous edema coma may appear (rare). There is also a significant proportion of hypothyroid patients without any symptoms. Diagnosis: The main laboratory tests are laboratory tests, and the commonly used tests13 are to check serum TSH, FT3, FT4. In hypothyroidism, the thyrotropin TSH secreted by the pituitary gland is significantly higher than normal, the thyroid hormones T4 and FT4 secreted by the thyroid gland in the blood are lower than normal, and T3 and FT3 can be normal in patients with mild disease, but significantly lower in patients with severe disease. In some hypothyroid patients without any symptoms, only TSH may be elevated in the blood (subclinical hypothyroidism). In a few patients, the lesion is not in the thyroid but in the pituitary gland or hypothalamus, in which case both TSH and thyroid hormones are reduced in the blood. In patients with Hashimoto’s thyroiditis, the TGAb and TPOAb are mostly positive. Treatment: The main treatment for hypothyroidism is thyroxine replacement therapy. Currently, dry thyroid tablets and levothyroxine tablets (such as thyroxine tablets and euthyroxine) are commonly used in China, which are satisfactory, inexpensive and easy to take. Start with a small dose and gradually increase the dose according to the systemic symptoms and laboratory tests until the systemic symptoms disappear and T3, T4, FT3, FT4 and TSH return to normal. Thereafter, maintain this dose for life and do not stop the drug easily, otherwise, the original disappeared symptoms may appear again within 1 to 3 months. If symptoms such as panic, arrhythmia, insomnia, irritability and excessive sweating appear during treatment, the dose should be reduced or checked at the hospital. If you forget to take the medication once in a while, there is no need to make up for it, and there is no need to increase the dosage when you take the medication next time, just still take it according to the previous dosage. In addition, even if all the symptoms disappear after taking the medication, you should go to the hospital regularly to recheck the level of thyroid hormone in your body and adjust the medication dose appropriately according to the test results, usually once every one to two years. Most hypothyroidism is a permanent disease and requires lifelong medication. Only a small percentage of hypothyroidism, such as subacute thyroiditis and drug-induced hypothyroidism, can be cured after treatment. Early onset hypothyroidism refers to hypothyroidism that occurs within one year after 131I treatment of hyperthyroidism. Most of this hypothyroidism can be restored to normal after conditioning and treatment, and a few can be permanent. Late onset hypothyroidism generally refers to hypothyroidism that occurs 1 year after 131I treatment, which is often permanent and requires lifelong replacement therapy. Patients with thyroid cancer need lifelong medication and regular review.