Depression is a common mental disorder characterized by depressed mood and loss of interest or pleasure. It is the leading cause of disability worldwide and has a high prevalence among women. Risk factors include genetics, brain chemistry, life stressors, and medical illnesses. Symptoms can range from mild to severe and include feelings of sadness, fatigue, changes in appetite, and suicidal thoughts in more severe cases. Treatment involves antidepressant medication, psychotherapy, or electroconvulsive therapy for severe or treatment-resistant cases. Antidepressants take 2-4 weeks to work and should be taken for at least 6-9 months after an initial episode or for 2 years for recurrent depression to prevent relapse.