Depression, also known as depressive disorder, is characterized by significant and persistent depression and is the main type of mood disorder. The depressed mood can range from sullenness to grief, low self-esteem and depression, or even pessimism and anxiety, and may include suicide attempts or behaviors; some cases have significant anxiety and motor agitation; severe cases may have hallucinations, delusions and other psychotic symptoms. Each episode lasts at least 2 weeks, or even several years. Most cases have a tendency to have recurrent episodes, and most of them can be relieved. Many biological, psychological and social environmental factors are involved in the pathogenesis of depression. Biological factors mainly involve genetic, neurobiochemical, neuroendocrine, and neuroregenerative aspects; psychological predisposing qualities that are closely related to depression are pre-morbid personality traits, such as depressive temperament. The exposure to stressful life events in adulthood is an important trigger for the development of clinically significant depressive episodes. However, these factors do not act in isolation, and the interaction between genetic and environmental or stressful factors, and the point at which this interaction occurs, are now emphasized as having an important influence in the development of depression. Clinical manifestations Depression can be manifested as a single or repeated multiple depressive episodes. 1, depressed mood Mainly manifested as significant and persistent depressed emotion, depression and pessimism. The lighter ones are sullen, unpleasant, and have diminished interest, while the heavier ones are in pain, pessimistic and desperate, living like a year, and life is worse than death. The typical patient’s depressed state of mind has a rhythmical change of heavy morning and light night. On the basis of depressed mood, patients will have reduced self-evaluation, a sense of uselessness, hopelessness, helplessness and worthlessness, often accompanied by self-blame and self-culpability, and in severe cases, delusions of guilt and paranoia, and some patients may experience hallucinations. 2. Slow thinking Patients have slow thinking and association, slow reaction, closed thinking, and feel that “the brain is like a rusty machine” and “the brain is like a layer of glue”. Clinically, the active speech is reduced, the speed of speech is significantly slowed, the voice is low, and it is difficult to answer, and in severe cases, communication cannot be carried out smoothly. 3.Decreased volitional activity The patient’s volitional activity is significantly and persistently inhibited. Clinical behavior is slow, life is passive, lazy, do not want to do anything, do not want to contact with the surrounding people, often sitting alone, or lying in bed all day, living alone behind closed doors, alienating friends and relatives, avoiding social interaction. In severe cases, the patient may even disregard physiological needs such as eating, drinking and personal hygiene, and may even develop into silent, immobile and non-eating, which is called “depressive rigidity”, but on careful mental examination, the patient still shows painful depression. Patients with anxiety may have symptoms such as fidgeting, finger grasping, hand rubbing or pacing around. Severe cases are often accompanied by negative suicidal ideation or behavior. Negative pessimistic thoughts and self-blame, lack of self-confidence can lead to desperate thoughts, thinking that “ending one’s life is a kind of relief”, “one is redundant in the world”, and can make suicide attempts develop into suicidal behavior. This is the most dangerous symptom of depression and should be vigilant. 4, cognitive impairment Research has concluded that depressed patients have cognitive impairment. This is mainly manifested as decreased near memory, attention deficit, prolonged reaction time, increased alertness, poor abstract thinking, learning difficulties, poor language fluency, reduced spatial perception, eye-hand coordination and flexibility of thinking. Cognitive impairment leads to social dysfunction and affects the long-term prognosis of patients. 5.Somatic symptoms include sleep disturbance, fatigue, loss of appetite, weight loss, constipation, pain in any part of the body, loss of libido, impotence, amenorrhea, etc. The physical complaints of somatic discomfort can involve all organs, such as nausea, vomiting, heartburn, chest tightness, sweating, etc. Symptoms of autonomic dysfunction are also more common. The complaints of pre-morbid somatic disorders are usually aggravated. Sleep disorders mainly manifest as early awakening, usually 2 to 3 hours earlier than usual, and inability to fall back to sleep after waking, which is characteristic for depressive episodes. Some present with difficulty falling asleep and not sleeping deeply; a few patients present with excessive sleep. Weight loss is not necessarily proportional to appetite loss, and a few patients may show increased appetite and weight gain. Examination For patients suspected of depression, in addition to a comprehensive physical examination and neurological examination, attention should be paid to the auxiliary examination and laboratory tests. To date, there are no specific tests for depressive disorders. Therefore, current laboratory tests are mainly designed to exclude depression due to substance and somatic disorders. There are 2 laboratory tests of some significance, including the dexamethasone suppression test (DST) and the thyrotropin-releasing hormone suppression test (TRHST). Diagnosis The diagnosis of depression should be mainly based on medical history, clinical symptoms, disease duration and physical examination and laboratory tests, and the diagnosis of typical cases is generally not difficult. At present, the common international diagnostic criteria are ICD-10 and DSM-IV. ICD-10 is mainly used in China, which refers to the first episode of depression and recurrent depression, excluding bipolar depression. Patients usually have typical symptoms such as depressed mood, loss of interest and pleasantness, low energy or fatigue. Other common symptoms are (1) decreased ability to focus and pay attention; (2) decreased self-evaluation; (3) self-guilt and feelings of worthlessness (even in mild episodes); (4) perception of a bleak and pessimistic future; (5) self-injurious or suicidal thoughts or behaviors; (6) sleep disturbances; and (7) decreased appetite. The duration of the illness lasts at least 2 weeks. V. Treatment 1. Treatment goals The treatment of depressive episodes should achieve three goals: (1) to improve the clinical cure rate, minimize the disability rate and suicide rate, the key is to completely eliminate clinical symptoms; (2) to improve the quality of survival and restore social function; (3) to prevent relapse. 2, treatment principles (1) individualized treatment; ② gradually increase the dose, as far as possible, using the minimum effective amount, so as to minimize adverse reactions, in order to improve compliance; ③ full amount of treatment; ④ as far as possible, a single drug, such as poor efficacy can be considered for conversion therapy, booster therapy or combination therapy, but need to pay attention to drug interactions; ⑤ informed before treatment; ⑥ closely observe the changes in the condition and adverse reactions during treatment and timely management; ⑦ adverse reactions; ⑤ informed before treatment; ⑥ closely observe the changes in the condition and (6) closely observe the changes and adverse reactions during the treatment and deal with them in time; (7) combine with psychotherapy to increase the efficacy; (8) actively treat other somatic diseases, substance dependence, anxiety disorders, etc. that are co-morbid with depression. Medication Medication is the main treatment for moderate depressive episodes or above. At present, the first-line antidepressants mainly include selective 5-hydroxytryptamine reuptake inhibitors (SSRI, representing drugs fluoxetine, paroxetine, sertraline, fluvoxamine, citalopram and escitalopram), 5-hydroxytryptamine and norepinephrine reuptake inhibitors (SNRI, representing drugs venlafaxine and duloxetine), norepinephrine and specific 5-hydroxytryptaminergic antidepressants (NaSSA, representing the drug mirtazapine), etc. Traditional tricyclic and tetracyclic antidepressants and monoamine oxidase inhibitors have been significantly reduced due to their large adverse effects. For patients with depressive episodes with obvious psychosocial factors, it is often necessary to combine psychotherapy with pharmacotherapy. Commonly used psychotherapy methods include supportive psychotherapy, cognitive-behavioral therapy, interpersonal therapy, marriage and family therapy, psychodynamic therapy, etc. Among them, the efficacy of cognitive-behavioral therapy on depressive episodes has been recognized. 5.Physical therapy Patients with severe negative suicidal attempts and those who have failed to be treated with antidepressants can be treated with modified electroconvulsive therapy (MECT). Maintenance treatment with medication is still required after electroconvulsive therapy. In recent years, a new physical therapy, repetitive transcranial magnetic stimulation (rTMS) therapy, has emerged and is mainly applied to mild to moderate depressive episodes. Prevention A study of depressed patients followed for 10 years found that 75% to 80% of patients had multiple relapses, so depressed patients need preventive treatment. More than 3 episodes should be treated for a long time, even lifelong medication. The dose of maintenance medication most scholars believe should be the same as the treatment dose, and should also be observed in regular outpatient follow-up visits. Psychotherapy and social support system also play a very important role in preventing relapse of the disease. Patients should be relieved or relieved of excessive psychological burden and pressure as much as possible, to help them solve practical difficulties and problems in life and work, to improve their coping ability, and to actively create a good environment for them to prevent relapse.