Hypothyroidism, also referred to as “low thyroid” or “hypothyroidism”, is a common clinical thyroid disorder that is more common in middle-aged women. Hypothyroidism is a systemic disease caused by insufficient synthesis and secretion or physiological effects of thyroid hormones. The disease starts insidiously, progresses slowly, and the early symptoms are not obvious, sometimes several years before the typical symptoms of hypothyroidism appear. 1, the cause of hypothyroidism: common causes of hypothyroidism in adults are: chronic lymphocytic thyroiditis (Hashimoto’s disease or autoimmune thyroiditis), previous thyroid surgery, hyperthyroidism after radioactive 131 iodine treatment, etc. Hypothyroidism in newborns is mostly congenital and often affects growth and development leading to “cretinism”. 2, the main manifestations of hypothyroidism: early symptoms are often manifested as fear of cold, weakness, drowsiness, poor nausea, constipation, menstrual disorders. With the progress of the disease, often appear cold, less sweating, slow speech and reaction, slow action, dry and thickened skin, rough and more flaky, hair loss, waxy face, swollen eyelids and cheeks, indifferent expression, dull, weight gain, brittle nails, low blood pressure, bradycardia. In severe cases, pericardial effusion, abdominal distension, constipation, generalized muscle aches and pains, and joint tonicity may occur. Most of them have decreased libido, male impotence, low menstrual flow in women, or amenorrhea in severe cases. If uncorrected for a long time, patients often have disorders of lipid metabolism, such as manifestations of hypercholesterolemia, hypertriglyceridemia, and even colic, heart failure, and mucus edema coma. 3, the diagnosis of hypothyroidism: one is based on clinical manifestations, the second is based on blood indicators. Definitive diagnosis must be based on serum thyroid hormone and thyroid stimulating hormone levels. The early stage of low thyroid often manifests as normal FT3, FT4 is reduced, TSH mildly elevated, with the aggravation of the disease, and not timely treatment, it manifests as FT3, FT4 are reduced, TSH significantly elevated. 4, low A treatment: low A treatment is relatively simple, but also very effective. The goal of the treatment is to adjust the thyroid function to the normal range through oral thyroxine replacement therapy to meet the metabolic needs of the body. The medication for low thyroid treatment is also relatively inexpensive, with domestic medication costing only a few cents a day and imported medication usually costing only a few cents a day, making it one of the least expensive diseases to treat. There are two main types of drugs available: (1) Thyroid tablets: They are prepared from the thyroid gland of animals (such as pigs and cows), and are therefore a crude form of thyroid tablets. Each tablet is 40 mg. Adults should take 1-3 tablets per day, and should be used under the guidance of a doctor according to the degree of low thyroid. The advantage of this drug is that it is inexpensive. The disadvantage is that the dose of thyroxine contained in the crude thyroid tissue is unstable and affects the effect, and one 40 mg tablet is not easily redivided. (2) Sodium levothyroxine (L-T4): At present, most of the imported “Uroxal”, each tablet is 50 micrograms, 100 micrograms two specifications. There are also domestic levothyroxine sodium tablets. The dose of this type of medicine is more stable and effective. Since one tablet can also be divided into 4 portions, it is easy to adjust the dose. The dose should be used according to the degree of hypothyroidism and should be directed by a doctor, usually ranging from 25 to 100 micrograms per day. Regardless of the type of thyroxine replacement therapy taken, serum FT3, FT4 and TSH should be routinely rechecked one month after the initial dose to adjust the dose according to the recovery of thyroid function, and thereafter the blood should be rechecked according to the situation. Since some hypothyroidism may recover on its own and some may further worsen, it should be reviewed regularly during treatment and if there is any discomfort, it should also be reviewed promptly.