A mental health disorder characterised by a persistently low mood or loss of interest in activities, resulting in significant impairment in daily life. A combination of biological, psychological, and social sources of distress are possible causes. These factors, according to research, may cause changes in brain function, including altered activity of certain neural circuits in the brain. Major depression is characterised by a persistent feeling of sadness or loss of interest, which can result in a variety of behavioural and physical symptoms. Changes in sleep, appetite, energy level, concentration, daily behaviour, or self-esteem are examples of these. Suicidal ideation is also associated with depression.

Medication, talk therapy, or a combination of the two is usually the mainstay of treatment. According to new research, these treatments may help to normalise brain changes associated with depression.