A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. The recognition and understanding of mental health conditions has changed over time and across cultures, and there are still variations in the definition, assessment, and classification of mental disorders, although standard guideline criteria are widely accepted. A few mental disorders are diagnosed based on the harm to others, regardless of the subject’s perception of distress. Over a third of people in most countries report meeting criteria for the major categories at some point in their lives.
The causes are often explained in terms of a diathesis-stress model or biopsychosocial model. In biological psychiatry, mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience.
Services are based in psychiatric hospitals or in the community. Diagnoses are made by psychiatrists or clinical psychologists using various methods, often relying on observation and questioning in interviews. Treatments are provided by various mental health professionals. Psychotherapy and psychiatric medication are two major treatment options, as are social interventions, peer support and self-help. In some cases there may be involuntary detention and involuntary treatment where legislation allows.
Stigma and discrimination add to the suffering associated with the disorders, and have led to various social movements attempting to increase acceptance.