What is depression and what are its main symptoms?

Health experts define depression as a common but serious mood disorder that affects thinking, feeling and daily functioning. According to the American Psychiatric Association and the World Health Organization, clinical depression, or major depressive disorder, is characterized by a persistently low mood or loss of interest in nearly all activities for at least two weeks. Dr. Maria Alvarez, a board-certified psychiatrist at a university medical center, explains that depression involves emotional, cognitive and physical symptoms that vary in severity. The core emotional symptoms include persistent sadness, feelings of worthlessness or excessive guilt, and a marked reduction in pleasure or interest, known as anhedonia. Cognitive symptoms often include difficulty concentrating, slowed thinking, indecisiveness, and recurrent thoughts of death or suicide. Physical signs can include changes in sleep — insomnia or hypersomnia — marked changes in appetite or weight, low energy or fatigue, and observable psychomotor agitation or retardation. Clinical guidelines emphasize duration and functional impairment; symptoms must cause significant distress or impairment and are not better explained by bereavement or another medical condition. Epidemiological data indicate depressive disorders affect hundreds of millions worldwide and are a leading cause of disability. Evidence-based treatments include psychotherapy, such as cognitive behavioral therapy, pharmacotherapy with antidepressants, and, for some, combined approaches; primary care screening and specialist referral improve outcomes. Experts urge anyone experiencing several of these symptoms for more than two weeks, especially suicidal thoughts, to seek immediate evaluation from a qualified clinician or crisis service. Trusted institutions recommend that family, employers and clinicians offer support, timely assessment and access to effective treatments to reduce burden and improve recovery. Public health initiatives that expand insurance coverage, integrate mental health into primary care, and reduce stigma have demonstrated measurable improvements in treatment rates and outcomes, according to peer-reviewed studies and national health agencies, and they support community-based programs.