Major depressive disorder (MDD), also known simply as depression, is a mental disorder characterized by at least two weeks of low mood that is present across most situations. It is often accompanied by low self-esteem, loss of interest in normally enjoyable activities, low energy, and pain without a clear cause. People may also occasionally have false beliefs or see or hear things that others cannot. Some people have periods of depression separated by years in which they are normal, while others nearly always have symptoms present. Major depressive disorder can negatively affect a person's personal life, work life, or education, as well as sleeping, eating habits, and general health. Between 2–8% of adults with major depression die by suicide, and about 50% of people who die by suicide had depression or another mood disorder.
A depressed person may report multiple physical symptoms such as fatigue, headaches, or digestive problems; physical complaints are the most common presenting problem in developing countries, according to the World Health Organization's criteria for depression. Appetite often decreases, with resulting weight loss, although increased appetite and weight gain occasionally occur. Family and friends may notice that the person's behavior is either agitated or lethargic. Older depressed people may have cognitive symptoms of recent onset, such as forgetfulness, and a more noticeable slowing of movements. Depression often coexists with physical disorders common among the elderly, such as stroke, other cardiovascular diseases, Parkinson's disease, and chronic obstructive pulmonary disease.
Depression and pain often co-occur. One or more pain symptoms are present in 65% of depressed patients, and anywhere from 5 to 85% of patients with pain will be suffering from depression, depending on the setting; there is a lower prevalence in general practice, and higher in specialty clinics. The diagnosis of depression is often delayed or missed, and the outcome can worsen if the depression is noticed but completely misunderstood.
HPA axis abnormalities have been suggested in depression given the association of CRHR1 with depression and the increased frequency of dexamethasone test non-suppression in depressed patients. However, this abnormality is not adequate as a diagnosis tool, because its sensitivity is only 44%. These stress-related abnormalities have been hypothesized to be the cause of hippocampal volume reductions seen in depressed patients. Furthermore, a meta-analysis yielded decreased dexamethasone suppression, and increased response to psychological stressors. Further abnormal results have been obscured with the cortisol awakening response, with increased response being associated with depression.
To confirm major depressive disorder as the most likely diagnosis, other potential diagnoses must be considered, including dysthymia, adjustment disorder with depressed mood, or bipolar disorder. Dysthymia is a chronic, milder mood disturbance in which a person reports a low mood almost daily over a span of at least two years. The symptoms are not as severe as those for major depression, although people with dysthymia are vulnerable to secondary episodes of major depression (sometimes referred to as double depression). Adjustment disorder with depressed mood is a mood disturbance appearing as a psychological response to an identifiable event or stressor, in which the resulting emotional or behavioral symptoms are significant but do not meet the criteria for a major depressive episode. Bipolar disorder, also known as manic–depressive disorder, is a condition in which depressive phases alternate with periods of mania or hypomania. Although depression is currently categorized as a separate disorder, there is ongoing debate because individuals diagnosed with major depression often experience some hypomanic symptoms, indicating a mood disorder continuum. Further differential diagnoses involve chronic fatigue syndrome.
Psychotherapy can be delivered to individuals, groups, or families by mental health professionals. A 2015 review found that cognitive behavioral therapy appears to be similar to antidepressant medication in terms of effect. A 2016 review found psychotherapy to be better than no treatment but not other treatments. With more complex and chronic forms of depression, a combination of medication and psychotherapy may be used. A 2014 Cochrane review found that work-directed interventions combined with clinical interventions helped to reduce sick days taken by people with depression. There is moderate-quality evidence that psychological therapies are a useful addition to standard antidepressant treatment of treatment-resistant depression in the short term.
A high proportion of people who experience full symptomatic remission still have at least one not fully resolved symptom after treatment. Recurrence or chronicity is more likely if symptoms have not fully resolved with treatment. Current guidelines recommend continuing antidepressants for four to six months after remission to prevent relapse. Evidence from many randomized controlled trials indicate continuing antidepressant medications after recovery can reduce the chance of relapse by 70% (41% on placebo vs. 18% on antidepressant). The preventive effect probably lasts for at least the first 36 months of use.
As with many other diseases, it is common among the elderly not to present with classical depressive symptoms. Diagnosis and treatment is further complicated in that the elderly are often simultaneously treated with a number of other drugs, and often have other concurrent diseases. Treatment differs in that studies of SSRIs have shown lesser and often inadequate effects among the elderly, while other drugs, such as duloxetine (a serotonin-norepinephrine reuptake inhibitor), with more clear effects have adverse effects, such as dizziness, dryness of the mouth, diarrhea and constipation, which can be especially difficult to handle among the elderly.