Educational summary
Overview
Major depressive disorder (MDD), commonly referred to as major depression or clinical depression, is a mental health disorder that can affect mood, thoughts, behavior, physical well-being, relationships, work, study, and other areas of daily life.
Depression can present differently from one person to another. Assessment therefore involves more than identifying a single symptom. Qualified health professionals consider the overall pattern, severity, duration, functional impact, medical history, medications and substances, and whether another mental health or medical condition may better explain the presentation.
Major depressive disorder is treatable. Appropriate care depends on the individual and may involve psychological treatment, medication, supportive interventions, or a combination of approaches.
This page is educational and is not intended to diagnose a mental health condition or replace evaluation by a qualified health professional.
References
- [1]What Is Depression?American Psychiatric AssociationAmerican Psychiatric Association — DepressionSupporting reference for the general educational overview.
- [2]Depressive disorder (depression)World Health Organization · 2025-08-29World Health Organization — DepressionKey factsSupporting reference for depression overview and treatment availability.
Educational summary
Signs and Symptoms
Depression can affect emotions, thinking, behavior, sleep, appetite, energy, physical activity, relationships, and everyday functioning.
Commonly recognized experiences can include:
- persistent sadness, emotional emptiness, or markedly lowered mood;
- reduced interest or enjoyment in activities;
- unusual tiredness or low energy;
- meaningful changes in sleep;
- changes in appetite or weight;
- difficulty concentrating, remembering, or making decisions;
- strong feelings of worthlessness or disproportionate guilt;
- noticeable slowing or increased restlessness;
- hopelessness or a strongly negative view of the future; and
- thoughts involving death, self-harm, or suicide.
People do not necessarily experience depression in the same way. Symptoms can vary in combination, intensity, presentation, and impact.
These experiences can also occur in other mental health conditions, medical conditions, medication effects, substance-related states, grief, sleep disorders, and other circumstances. For that reason, this information should not be used as a checklist to diagnose major depressive disorder.
Diagnosis requires an appropriate clinical assessment that considers the overall pattern of symptoms, their course and impact, relevant medical and mental health history, and alternative explanations.
References
- [1]DepressionNational Institute of Mental HealthNational Institute of Mental Health — DepressionWhat are the signs and symptoms of depression?Supporting source for the educational signs and symptoms summary.
- [2]Depressive disorder (depression)World Health Organization · 2025-08-29World Health Organization — DepressionSymptoms and patternsSupporting source for the educational signs and symptoms summary.
- [3]What Is Depression?American Psychiatric AssociationAmerican Psychiatric Association — DepressionSupporting source for the educational signs and symptoms summary.
Educational summary
Causes and Risk Factors
Major depressive disorder does not have a single known cause. Research indicates that depression can develop through interactions among genetic, biological, psychological, environmental, and social factors.
Factors associated with a greater likelihood of depression can include:
- a personal or family history of depression or other mental health conditions;
- stressful, traumatic, or otherwise adverse life experiences;
- bereavement, relationship disruption, unemployment, or other significant life stressors;
- chronic medical illness and the psychological or physical burdens associated with illness;
- certain medications, substances, or medical conditions that can contribute to depressive symptoms; and
- combinations of biological vulnerability and environmental stress.
A risk factor does not mean that a person will necessarily develop major depressive disorder. Some people develop depression without an obvious precipitating event, while others experience substantial adversity without developing the disorder.
Clinical evaluation considers the person's history and circumstances rather than attempting to identify one universal cause.
References
- [1]Depressive disorder (depression)World Health Organization · 2025-08-29World Health Organization — DepressionContributing factors and preventionSupporting source for contributing-factor and adverse-life-event information.
- [2]Understanding the Link Between Chronic Disease and DepressionNational Institute of Mental HealthNational Institute of Mental Health — Chronic Illness and Mental HealthCan chronic disease lead to depression?Supporting source for chronic illness and depression risk information.
Educational summary
Related and Co-occurring Conditions
Depressive symptoms are not unique to major depressive disorder. Similar symptoms may appear in other psychiatric conditions, medical illnesses, medication effects, substance-related states, sleep disorders, grief, and other circumstances.
One particularly important distinction is between unipolar depression and bipolar disorders. People with bipolar I or bipolar II disorder can experience depressive episodes, so assessment may include questions about previous periods of unusually elevated or irritable mood, increased energy, reduced need for sleep, or other features associated with mania or hypomania.
Depression can also occur alongside other mental health disorders. Anxiety disorders and post-traumatic stress disorder are examples of conditions that may coexist with depressive symptoms.
Differential diagnosis requires professional assessment. The relationships presented on this website are educational and are not an exhaustive diagnostic algorithm.
References
- [1]Bipolar DisorderNational Institute of Mental HealthNational Institute of Mental Health — Bipolar DisorderWhat is bipolar disorder?Supporting source for bipolar depressive episodes and differential-diagnosis context.
- [2]Generalized Anxiety Disorder: What You Need to KnowNational Institute of Mental HealthNational Institute of Mental Health — Generalized Anxiety DisorderWhat is generalized anxiety disorder?Supporting source for depression and anxiety co-occurrence.
- [3]Post-Traumatic Stress DisorderNational Institute of Mental HealthNational Institute of Mental Health — PTSDWhat is post-traumatic stress disorder, or PTSD?Supporting source for PTSD and depression co-occurrence.
- [4]DepressionNational Institute of Mental HealthNational Institute of Mental Health — DepressionWhat are the different types of depression?Supporting source for co-occurring mental and physical conditions.
Educational summary
Treatment
Major depressive disorder is treatable, and treatment should be individualized according to the person's symptoms, severity, preferences, previous treatment response, medical history, other health conditions, safety considerations, and access to care.
Evidence-based treatment approaches can include psychological therapies and antidepressant medication. Psychological approaches used in depression include cognitive behavioral therapy, behavioral activation, interpersonal psychotherapy, and other structured therapies.
Medication may be considered depending on the clinical situation. Decisions about starting, changing, combining, or stopping medication should be made with an appropriately qualified health professional who can consider potential benefits, adverse effects, interactions, monitoring needs, and individual circumstances.
For some people, particularly when depression is severe or has not responded adequately to standard treatments, specialist options can include brain-stimulation treatments such as electroconvulsive therapy or repetitive transcranial magnetic stimulation.
Treatment information on this website is educational. It does not recommend a specific treatment for an individual and does not replace assessment by a qualified health professional.
References
- [1]Depressive disorder (depression)World Health Organization · 2025-08-29World Health Organization — DepressionDiagnosis and treatmentSupporting source for psychological and medication treatment information.
- [2]DepressionNational Institute of Mental HealthNational Institute of Mental Health — DepressionHow is depression treated?Supporting source for psychotherapy, medication, and other depression treatment information.
- [3]Depression in adults: treatment and managementNational Institute for Health and Care Excellence · 2022-06-29NICE NG222 — Depression in adultsRecommendationsSupporting clinical guideline for adult depression treatment and management.
- [4]Brain Stimulation TherapiesNational Institute of Mental HealthNational Institute of Mental Health — Brain Stimulation TherapiesWhat is electroconvulsive therapy?Supporting source for ECT and transcranial magnetic stimulation information.
Associated features
Symptoms
- Persistently Low or Depressed Moodassociated
An ongoing experience of sadness, emotional heaviness, emptiness, or markedly lowered mood.
Depressed or markedly lowered mood may occur as part of a depressive presentation.
- Reduced Interest or Pleasureassociated
A noticeable reduction in interest, enjoyment, motivation, or pleasure in activities that would ordinarily be engaging or rewarding.
Reduced interest, enjoyment, or pleasure may affect hobbies, relationships, work, study, or other activities.
- Low Energy or Fatigueassociated
Reduced energy, unusual tiredness, or a sense that ordinary physical or mental activities require substantially more effort.
Depressive presentations can involve substantial fatigue or reduced physical and mental energy.
- Sleep Disturbanceassociated
A meaningful change in usual sleep, which may include difficulty sleeping, disrupted sleep, waking unusually early, or sleeping substantially more than usual.
Sleep patterns may shift in either direction and should be interpreted in the context of the overall presentation.
- Appetite or Weight Changeassociated
A noticeable change in appetite, food intake, or body weight that occurs alongside a change in mental health.
Changes in appetite or weight can occur alongside depression but can also have medical and other explanations.
Difficulty sustaining attention, organizing thoughts, remembering information, or making everyday decisions.
Attention, memory, thinking efficiency, and decision-making can be affected during depression.
Persistent or disproportionate negative judgments about oneself, including strong feelings of worthlessness, failure, or guilt.
Negative self-evaluation, worthlessness, or disproportionate guilt may accompany depressive states.
- Psychomotor Slowing or Restlessnessassociated
Observable or subjectively experienced changes in physical activity, such as unusual slowing or increased restlessness and difficulty remaining still.
Some people experience noticeable slowing of activity while others experience increased agitation or restlessness.
- Hopelessness or Pessimismassociated
A persistent expectation that circumstances are unlikely to improve or that the future holds little possibility of positive change.
Depression may substantially affect expectations about the future and the perceived possibility of improvement.
- Thoughts of Death, Self-Harm, or Suicideassociated
Thoughts concerning death, self-injury, or suicide. Such experiences can represent an urgent safety concern and warrant appropriate professional assessment.
Thoughts involving death, self-harm, or suicide require careful safety assessment and should not be treated as an ordinary website self-diagnosis item.
Reference systems
Classifications
- System
- Diagnostic and Statistical Manual of Mental Disorders (DSM-5-TR)
- Classification
- Major Depressive Disorder
- Category
- Depressive Disorders
- Source
- Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR)
- System
- International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
- Classification
- Major depressive disorder, recurrent
- Code
- F33
- Category
- Mental, Behavioral and Neurodevelopmental disorders
- Source
- International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
- System
- International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
- Classification
- Major depressive disorder, single episode
- Code
- F32
- Category
- Mental, Behavioral and Neurodevelopmental disorders
- Source
- International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
Treatment reference
Treatments
- Cognitive Behavioral Therapypsychotherapy
A structured psychological therapy focused on relationships among thoughts, emotions, behaviors, and coping patterns.
Psychological treatment option.
Recognized evidence-based psychological treatment used in the management of depression.
- Behavioral Activationpsychotherapy
A psychological treatment approach focused on increasing engagement with meaningful or reinforcing activities and reducing patterns that may maintain depression.
Psychological treatment option.
Recognized psychological treatment used in the management of depression.
- Interpersonal Psychotherapypsychotherapy
A structured psychological therapy focused on interpersonal relationships, life changes, grief, and related difficulties associated with depressive symptoms.
Psychological treatment option.
Recognized psychological treatment used in the management of depression.
- Antidepressant Medicationmedication_class
A broad category of prescription medicines used in the treatment of depressive disorders. Selection and monitoring require individualized clinical assessment.
Medication treatment category requiring clinician-led selection and monitoring.
Antidepressant medicines are an established treatment option for depression; appropriateness depends on clinical presentation, severity, preferences, risks, previous response, and other individual factors.
A noninvasive brain-stimulation treatment that uses magnetic stimulation and is used in the treatment of some depressive conditions.
Noninvasive brain-stimulation treatment used in selected clinical circumstances.
rTMS is a noninvasive brain-stimulation approach used in depression, including in some people who have not had sufficient benefit from other treatments.
- Electroconvulsive Therapyprocedure
A medical brain-stimulation treatment used for some severe or otherwise clinically appropriate depressive presentations.
Specialist brain-stimulation treatment used in selected clinical circumstances.
ECT is an established brain-stimulation treatment that may be considered for severe depression or other situations where specialist treatment is appropriate.
Evidence & references
Sources
- What Is Depression?American Psychiatric Association
- Depressive disorder (depression)World Health Organization · 2025-08-29
- DepressionNational Institute of Mental Health
- Understanding the Link Between Chronic Disease and DepressionNational Institute of Mental Health
- Bipolar DisorderNational Institute of Mental Health
- Generalized Anxiety Disorder: What You Need to KnowNational Institute of Mental Health
- Post-Traumatic Stress DisorderNational Institute of Mental Health
- Depression in adults: treatment and managementNational Institute for Health and Care Excellence · 2022-06-29
- Brain Stimulation TherapiesNational Institute of Mental Health