Depressive disorder is a common mood disorder that can be caused by a variety of reasons, with significant and persistent depression as the main clinical feature, and the depression is not proportional to its situation, the clinical manifestations can range from sullenness to grief, and even the occurrence of wood stiffness; some cases have obvious anxiety and motor agitation; severe cases can appear hallucinations, delusions and other psychotic symptoms. Most cases have a tendency to have recurrent episodes, with each episode mostly resolving, and some may have residual symptoms or become chronic. The main symptoms include: depression, dysphoria, psychogenic depression, depression associated with brain or somatic disorders, depression associated with psychoactive or non-addictive substance-induced psychiatric disorders, and post-psychotic depression.