Depression is no less dangerous to human life than car accidents and war, because the most tragic end of untreated depression is suicide and death. The author has personally experienced that there are many patients with depression in general hospitals in the departments of internal and external medicine and other somatic diseases. In fact, depression has become the disease of the century in the 21st century. I. Etiology 5-HT hypothesis, norepinephrine hypothesis, dopamine hypothesis, acetylcholine hypothesis, r-aminobutyric acid hypothesis, etc. have theoretical and practical basis. Neuroendocrine dysregulation theory, and neuroplasticity studies, neurophysiological studies, and neuroimaging studies have progressed, but none of the mechanisms have been elucidated. Psychosocial factors are undeniable as one of the etiologies of depression. Evidence from multiple studies suggests that genetic qualities play an important role in major depressive disorder. However, the role of genetic factors for some mild depression or atypical depression or poor mood seems to be less certain or obvious. Clinical manifestations The core symptoms of depression are currently considered to include depressed mood, lack of interest and pleasure, and may be accompanied by somatic symptoms and suicidal behavior. 1. Depressed mood: Patients feel depressed or depressed, even if they encounter something pleasant, they cannot be happy. 2, pessimistic disappointment: the patient thinks of the present and has a sense of uselessness and helplessness, a sense of hopelessness when considering the future, and a sense of self-blame and self-guilt when reflecting on the past. 3. Reduced or absent interest, diminished energy, and slowed action: Patients feel general weakness, often become disinterested in their previous daily work and hobbies, no longer enthusiastic about daily life and various activities, and feel meaningless. Patients feel that their bodies are heavy, they have difficulty in making associations, they struggle to think about problems, and they give the impression of being unresponsive. In severe cases, the patient may sit in silence all day long. 4. Patients with pleasure deficit lose the ability to experience happiness. We usually have joy, anger and sadness for everyone, but depressed patients often cannot experience pleasure and fun from daily life and laugh happily. Some patients also seem to also do some activities, such as watching TV, dancing in the street group dance, but his purpose is to fight against worries, kill time, reduce worries, hoping to be relieved from the predicament, there is no pleasure to speak of. 5, other common symptoms: sleep disorders such as difficulty falling asleep, easy to wake up and early awakening, the most characteristic is early awakening in the early morning, some patients will have the opposite performance is increased sleep. Depressed mood, pessimism and disappointment day and night. Loss of appetite and weight loss, loss of sexual desire or loss, chest tightness and shortness of breath, sighing, dry and bitter mouth, loss of appetite, nausea, vomiting, abdominal distention, and constipation are common. In contrast, headache, dizziness, palpitations, panic, sweating, chest tightness, hot and cold sensation and tingling of the skin, and urinary frequency and urgency are mostly seen in mild depression. Somatic complaints and symptoms of suspicion, pain or discomfort in various parts of the body are also more frequent in mild depression. 6. The most common symptoms in some patients with mild or moderate depression (about twice as many women as men) are: general weakness, easy fatigue, persistent headache or chronic pain and vague discomfort in other parts of the body, abdominal discomfort, loss of appetite, anorexia, weight loss, nausea, vomiting, dry mouth, constipation, loose diarrhea, urination disorder, chest stuffiness, dizziness, tinnitus, loss of libido, menstrual The patients often have suspicion first. Patients often have a suspicion that they are suffering from hepatitis, lung cancer, pleurisy, gastric disease, etc. Some patients ask their doctors to repeatedly examine them because they are afraid that it is heart disease or cancer. Many such patients are often misdiagnosed with multiple diseases. Due to the prominence of the above symptoms, patients always initially seek treatment from internal, external, Chinese medicine and other doctors, and have undergone many tests and even surgery, but the treatment is always poor, and some patients are even diagnosed as disease-free when they visit the doctor. Therefore, for those who have more complaints of somatic symptoms mentioned above and do not match with somatic factors, the possibility of depression should be thought of, and detailed examination by psychiatrists can often reveal traces of depression. 7.Severe depression can have a series of psychiatric symptoms such as delusions of guilt, delusions of suspicion, delusions of poverty, hallucinations, and in severe cases, depressive rigidity can also appear. Diagnosis and treatment Depression seriously affects the quality of human life, insomnia, anxiety, depression, and even suicide seriously threaten human health. Diagnosis by psychiatrists or mental health experts is very necessary. In recent years, many new antidepressants have been developed and used more and more widely. However, their use still needs to be guided by a professional physician to avoid serious problems, cure into disease, and regret.