Major depressive disorder (MDD), also known simply as depression, is a mental disorder characterized by at least two weeks of pervasive low mood. Low self-esteem, loss of interest in normally enjoyable activities, low energy, and pain without a clear cause are common symptoms. Those affected may also occasionally have delusions or hallucinations. Some people have periods of depression separated by years, while others nearly always have symptoms present. Major depression is more severe and lasts longer than sadness, which is a normal part of life.The diagnosis of major depressive disorder is based on the person's reported experiences and a mental status examination. There is no laboratory test for the disorder, but testing may be done to rule out physical conditions that can cause similar symptoms. Those with major depressive disorder are typically treated with counseling and antidepressant medication. Medication appears to be effective, but the effect may only be significant in the most severely depressed. Types of counseling used include cognitive behavioral therapy (CBT) and interpersonal therapy, and electroconvulsive therapy (ECT) may be considered if other measures are not effective. Hospitalization may be necessary in cases with a risk of harm to self and may occasionally occur against a person's wishes.The most common time of onset is in a person's 20s and 30s, with females affected about twice as often as males. Major depressive disorder affected approximately 163 million people (2% of the world's population) in 2017. The percentage of people who are affected at one point in their life varies from 7% in Japan to 21% in France. Lifetime rates are higher in the developed world (15%) compared to the developing world (11%). The disorder causes the second-most years lived with disability, after lower back pain.The term major depressive disorder was introduced by a group of US clinicians in the mid-1970s. The cause of major depressive disorder is believed to be a combination of genetic, environmental, and psychological factors, with about 40% of the risk related to genetics. Risk factors include a family history of the condition, major life changes, certain medications, chronic health problems, and substance use disorders. It can negatively affect a person's personal life, work life, or education as well as sleeping, eating habits, and general health. Those currently or previously affected with the disorder may be stigmatized.