Major depression, also known as clinical depression or unipolar depression, is a mental disorder characterized by an overwhelming low mood as well as low self esteem and loss of interest or pleasure in normally enjoyable activities. Sufferers lack energy and are unable to concentrate; they feel irritable for no apparent reason, and experience feelings of hopelessness, inappropriate guilt or regret and self-hatred.

If the deep sense of sadness lasts for longer than two weeks and begins to affect family, work and social life as well as eating and sleeping habits and general health, then a person may be suffering from major depression. In severe cases sufferers may have delusions or hallucinations. A small number of sufferers will commit suicide, and a high percentage of those who commit suicide have depression.

Most people will experience bouts of depression more than once, yet many will never seek help even though the majority will respond to treatment. The most common age for the onset of symptoms is between 30 and 40 years old, with another peak between 50 and 60.

Diagnosis of the illness is mostly done by self- reports and evidence provided by friends and family, and a mental status exam, which assesses the person’s current mood and thoughts, is also used to assess the level of the illness.

Patients are treated with antidepressants which has a high response rate. It can take up to eight weeks from the start of treatment to remission, when the patient is back to their normal self, and the drugs will continue to be prescribed up to 20 weeks after remission to minimise the chance of a reoccurrence. Those with chronic depression may need to continue their medication for the rest of their lives to avoid a relapse.

Psychotherapy and counselling is also used to treat depression, and many doctors recommend exercise with results showing this to be beneficial. Hospitalisation may be necessary if sufferers are deemed to be at risk of harming themselves or others. Those with depression have shorter life expectancies than those without because they are more susceptible to other medical illnesses like heart disease. Sufferers are also more likely to report physical pain in their bodies.

Drug and alcohol use greatly increases the risk of depression, but more research is still being carried out to find out the exact causes of depression, with evolutionary, biological, hereditary and difficult social situations like poverty or isolation reasons that have been cited.