Hypothyroidism has an insidious onset and a long course. Most patients do not have specific signs and symptoms, mainly characterized by decreased metabolic rate and decreased sympathetic excitability, but some patients may also develop serious complications. Hypothyroidism can affect various systems of the whole body: the thyroid gland itself: it can be atrophic or enlarged, and some patients with primary hypothyroidism can have enlarged pituitary gland if they do not receive timely treatment, and some transient hypothyroidism may develop into lifelong hypothyroidism if it is not handled properly. Digestive system: Gastrointestinal edema, decreased metabolism and weight gain may occur. Poor sense of taste, atrophy of gastric mucosa, decreased gastric acid secretion. Gastrointestinal peristalsis is weakened and constipation occurs. Cardiovascular system: decreased myocardial contractility, decreased cardiac output, decreased activity tolerance. In severe cases, heart failure and pericardial effusion may occur. Respiratory system: hypoventilation, sleep apnea, also snoring and sleep apnea due to edema. Hematologic system: normocytic, normochromic anemia, decreased hematocrit. Nervous system: apathy, prolonged reflexes, lethargy, drowsiness. Reproductive system: decreased fertility, libido. Menstrual disorders or heavy menstruation in women. Other endocrine system: hypothyroidism-primary hypoadrenalism (Schmidt’s syndrome). Hypopituitarism. Mucous edema coma: it is the end-stage manifestation of patients with hypothyroidism who have not received effective treatment for a long period of time, and it is a serious state in which the condition of hypothyroidism is aggravated, which is mostly induced by infections and the use of tranquilizers and so on. Clinical manifestations are drowsiness, mental abnormality, stiffness and even coma, which often occurs in elderly patients with hypothyroidism accompanied by cardiopulmonary diseases, with a poor prognosis and a mortality rate of about 20%. Other manifestations: low metabolism of various intermediates, reduced enzyme clearance, increased concentrations of cholesterol, triglycerides, low-density lipoproteins, muscle enzymes. Skin dryness, dermal mucopolysaccharide infiltration, body fluid storage. In severe cases, mucous edema can occur. Therefore, the harm of addition and subtraction is multifaceted, some even life-threatening, patients must not pay attention to medical treatment because the symptoms are not obvious.