The document discusses depression, including its symptoms, common causes, and relationship with substance abuse. Depression is defined as feeling down for over two weeks to the point where it interferes with daily life and can include symptoms like low energy, poor concentration, irritability, low self-esteem, hopelessness, changes in appetite and sleep. Common causes of depression include genetics/family history, stress from life events, a pessimistic personality, physical illnesses, and other psychological disorders. The document notes that depression can lead to substance abuse as people may use drugs and alcohol to self-medicate symptoms, but this actually makes depression worse over time.