DSM and ICD criteria
The most widely used criteria for diagnosing depressive conditions are found in the American Psychiatric Associations Diagnostic and Statistical Manual of Mental Disorders (DSM) and the World Health Organizations International Statistical Classification of Diseases and Related Health Problems (ICD). The latter system is typically used in European countries, while the former is used in the US and many other non-European nations, and the authors of both have worked towards conforming one with the other. Both DSM and ICD mark out typical (main) depressive symptoms. The most recent edition of the DSM is the Fifth Edition, Text Revision (DSM-5-TR), and the most recent edition of the ICD is the Eleventh Edition (ICD-11).Under mood disorders, ICD-11 classifies major depressive disorder as either single episode depressive disorder (where there is no history of depressive episodes, or of mania) or recurrent depressive disorder (where there is a history of prior episodes, with no history of mania). ICD-11 symptoms, present nearly every day for at least two weeks, are a depressed mood or anhedonia, accompanied by other symptoms such as "difficulty concentrating, feelings of worthlessness or excessive or inappropriate guilt, hopelessness, recurrent thoughts of death or suicide, changes in appetite or sleep, psychomotor agitation or retardation, and reduced energy or fatigue." These symptoms must affect work, social, or domestic activities.
Other health problems
Depression can also arise after a chronic or terminal medical condition, such as HIV/AIDS or asthma, and may be labeled "secondary depression." It is unknown whether the underlying diseases induce depression through effect on quality of life, or through shared etiologies (such as degeneration of the basal ganglia in Parkinsons disease or immune dysregulation in asthma). Depression may also be iatrogenic (the result of healthcare), such as drug-induced depression. Therapies associated with depression include interferons, beta-blockers, isotretinoin, contraceptives, cardiac agents, anticonvulsants, antimigraine drugs, antipsychotics, and hormonal agents such as gonadotropin-releasing hormone agonist. Substance use in early age is associated with increased risk of developing depression later in life. Depression occurring after giving birth is called postpartum depression and is thought to be the result of hormonal changes associated with pregnancy. Seasonal affective disorder, a type of depression associated with seasonal changes in sunlight, is thought to be triggered by decreased sunlight. Vitamin B2, B6 and B12 deficiency may cause depression in females. Pathophysiology
The pathophysiology of depression is not completely understood, but current theories center around monoaminergic systems, the circadian rhythm, immunological dysfunction, HPA-axis dysfunction and structural or functional abnormalities of emotional circuits. Derived from the effectiveness of monoaminergic drugs in treating depression, the monoamine theory posits that insufficient activity of monoamine neurotransmitters is the primary cause of depression. Evidence for the monoamine theory comes from multiple areas.