Even today, people’s conceptualizations of depression vary widely, both within and among cultures. “Because of the lack of scientific certainty,” one commentator has observed, “the debate over depression turns on questions of language. What we call it—’disease,’ ‘disorder,’ ’state of mind’—affects how we view, diagnose, and treat it.” There are cultural differences in the extent to which serious depression is considered an illness requiring personal professional treatment, or is an indicator of something else, such as the need to address social or moral problems, the result of biological imbalances, or a reflection of individual differences in the understanding of distress that may reinforce feelings of powerlessness, and emotional struggle.

The Ancient Greek physician Hippocrates described a syndrome of melancholia as a distinct disease with particular mental and physical symptoms; he characterized all “fears and despondencies, if they last a long time” as being symptomatic of the ailment. It was a similar but far broader concept than today’s depression; prominence was given to a clustering of the symptoms of sadness, dejection, and despondency, and often fear, anger, delusions and obsessions were included.

Major depressive episodes often resolve over time whether or not they are treated. Outpatients on a waiting list show a 10–15% reduction in symptoms within a few months, with approximately 20% no longer meeting the full criteria for a depressive disorder. The median duration of an episode has been estimated to be 23 weeks, with the highest rate of recovery in the first three months.

The three most common treatments for depression are psychotherapy, medication, and electroconvulsive therapy. Psychotherapy is the treatment of choice for people under 18, while electroconvulsive therapy is only used as a last resort. Care is usually given on an outpatient basis, while treatment in an inpatient unit is considered if there is a significant risk to self or others.

A diagnostic assessment may be conducted by a general practitioner or by a psychiatrist or psychologist, who will record the person’s current circumstances, biographical history and current symptoms, and a family medical history to see if other family members have suffered from a mood disorder, and discuss the person’s alcohol and drug use. The assessment also includes a mental state examination, which is an assessment of the person’s current mood and thought content, in particular the presence of themes of hopelessness or pessimism, self-harm or suicide, and an absence of positive thoughts or plans. Specialist mental health services are rare in rural areas, and thus diagnosis and management is largely left to primary care clinicians. This issue is even more marked in developing countries. Rating scales are not used to diagnose depression, but they provide an indication of the severity of symptoms for a time period, so a person who scores above a given cut-off point can be more thoroughly evaluated for a depressive disorder diagnosis. Several rating scales are used for this purpose. Screening programs have been advocated to improve detection of depression, but there is evidence that they do not improve detection rates, treatment, or outcome.

The biopsychosocial model proposes that biological, psychological, and social factors all play a role to varying degrees in causing depression. The diathesis–stress model posits that depression results when a preexisting vulnerability, or diathesis, is activated by stressful life events. The preexisting vulnerability can be either genetic, implying an interaction between nature and nurture, or the result of past experience such as learned views of the world formed in childhood. These interactive models to understanding the causes of depression have gained empirical support. For example, a prospective, longitudinal study uncovered a moderating effect of the serotonin transporter (5-HTT) gene on stressful life events in predicting depression. Specifically, depression may follow such events, but is more likely to in people with one or, even more so, two short alleles of the 5-HTT gene. A Swedish study estimated the heritability of depression (the degree to which individual differences in occurrence are associated with genetic differences) to be approximately 40% for women and 30% for men.

Major depression is a serious illness that affects a person’s family, work or school life, sleeping and eating habits, and general health; its impact on functioning and well-being has been equated to that of chronic medical conditions such as diabetes.