Depression
Also known as: major depressive disorder, MDD, clinical depression
Medically reviewed by Nano Health Insights Editorial Team · Last reviewed 2026-06-24
Depression is a mood disorder that causes persistent sadness or loss of interest for at least 2 weeks.
What it is
Depression is a mood disorder that causes persistent sadness or loss of interest for at least 2 weeks. In major depressive disorder, diagnosis generally requires 5 or more symptoms during the same 2-week period, and one of them must be depressed mood or markedly reduced interest or pleasure. Depression is more than a temporary low mood. It can affect sleep, appetite, energy, concentration, movement, work, relationships, and physical health, and it can include thoughts of death or suicide.
The term “depression” is often used broadly, but clinicians distinguish major depressive disorder (MDD) from other depressive disorders such as persistent depressive disorder, premenstrual dysphoric disorder, and depression caused by substances or another medical condition. Children and adolescents may show irritability rather than obvious sadness. Depression is common, serious, and treatable.
A simple way to think about core symptoms is:
| Core feature | What it can look like |
|---|---|
| Low mood | Sadness, emptiness, tearfulness, hopelessness |
| Loss of interest | No longer enjoying work, hobbies, food, sex, or social contact |
| Body symptoms | Sleep change, appetite change, fatigue, slowed movement or agitation |
| Thinking symptoms | Poor concentration, guilt, worthlessness, indecisiveness |
| Safety concern | Thoughts of death, self-harm, or suicide |
In India, depression is a major public health issue as well, with barriers that include stigma, limited access to mental health care in some areas, and under-recognition in primary care. Symptoms may first be described as body complaints such as fatigue, pain, headache, or poor sleep rather than as “feeling depressed.”
How it works
Depression does not have one single cause. It is usually understood as a condition that develops from a mix of biological, psychological, and social factors.
Biological factors can include family history, changes in brain circuits involved in mood and reward, hormonal shifts, chronic inflammation in some patients, and coexisting medical illnesses such as thyroid disease, diabetes, cardiovascular disease, Parkinson disease, or chronic pain. Psychological factors can include negative thinking patterns, trauma, grief, and poor coping strategies. Social factors can include isolation, financial stress, relationship conflict, violence, bereavement, and substance use.
Depression can also change how the brain and body respond to stress. Sleep-wake rhythms, appetite regulation, motivation, and attention may all be disrupted. This helps explain why depression often feels both emotional and physical.
Importantly, a history of mania or hypomania suggests bipolar disorder rather than unipolar major depression. That distinction matters because treatment choices differ.
Diagnosis / how it's measured
Depression is diagnosed clinically. There is no single blood test or brain scan that confirms MDD.
Clinicians usually diagnose major depressive disorder using DSM-5 criteria, history, mental status examination, and assessment of functioning and safety. Key points include symptom duration, severity, effect on daily life, past episodes, family history, substance use, and whether there have ever been manic or hypomanic symptoms.
Common screening tools include:
- PHQ-2: a brief 2-question screen.
- PHQ-9: a 9-item questionnaire often used in primary care to screen and track severity.
- Hamilton Depression Rating Scale (HAM-D) or similar clinician-rated scales in specialist settings.
Doctors may also order tests to look for contributors or mimics, such as anemia, thyroid disease, vitamin deficiencies, medication effects, alcohol or drug use, or other psychiatric conditions. Depression can occur alongside anxiety disorders, substance use disorders, and chronic medical illness.
A diagnosis should also include suicide risk assessment. Warning signs include suicidal thoughts, a plan, access to means, severe hopelessness, agitation, recent major loss, intoxication, or past suicide attempts.
Evidence and uses
Treatment depends on severity, safety, patient preference, prior response, access, and coexisting conditions. The best-supported treatments are psychotherapy, antidepressant medication, or both.
| Treatment | What it is used for | What evidence shows |
|---|---|---|
| Psychotherapy | Mild to severe depression | Cognitive behavioral therapy, interpersonal therapy, and behavioral activation can reduce symptoms and relapse risk |
| Antidepressants | Moderate to severe depression, recurrent depression, depression with marked functional impairment | Many antidepressants are effective on average, though individual response varies |
| Combined treatment | More severe, chronic, or recurrent depression | Often more effective than either treatment alone for some patients |
| ECT | Severe depression, psychotic depression, catatonia, urgent suicidality, treatment resistance | Among the most effective acute treatments, especially when rapid response is needed |
| Other options | Treatment-resistant cases | TMS, ketamine or esketamine, and augmentation strategies may help selected patients |
Lifestyle measures such as regular sleep, physical activity, reduced alcohol use, social support, and treatment of medical comorbidities can help, but they are not a substitute for professional care when depression is moderate, severe, persistent, or associated with suicidality.
Response to treatment usually takes time. Antidepressants often need several weeks before full benefit is clear. Some people need dose adjustment, switching, or augmentation. Continuing treatment after improvement lowers relapse risk.
Evidence in humans supports standard psychiatric treatments much more strongly than supplements or traditional remedies. Some complementary approaches are being studied, but results are mixed and they should not replace evidence-based care, especially in severe depression.
When to see a clinician
See a clinician if low mood, loss of interest, poor sleep, fatigue, hopelessness, or concentration problems last 2 weeks or more, keep coming back, or interfere with work, school, caregiving, or relationships. Seek care sooner if symptoms are severe, if there is substance misuse, or if depression occurs during pregnancy or after childbirth.
Get urgent help now if there are thoughts of suicide, self-harm, harming others, psychotic symptoms such as hearing voices, inability to care for basic needs, or extreme agitation. If someone is in immediate danger, contact local emergency services or a suicide crisis service right away.
Family members should take statements like “I want to die” seriously, even if the person later minimizes them.
Limitations and open questions
Depression is a broad diagnosis with many possible causes and symptom patterns, so no single treatment works for everyone. Current diagnosis still relies mainly on symptoms and clinical judgment rather than a definitive biomarker.
Researchers are studying why some people respond quickly to treatment while others have treatment-resistant depression, and whether biological markers, digital tools, or brain-based measures can guide more personalized care. Evidence is also evolving on newer treatments such as ketamine, neuromodulation, and strategies for relapse prevention.
Another limitation is underdiagnosis. Depression may be missed when it presents mainly with physical symptoms, anxiety, irritability, or substance use. Stigma and limited access to mental health services remain major barriers in many settings, including parts of India.
If depression is suspected, early assessment matters because effective treatment can reduce suffering, improve functioning, and lower suicide risk.
FAQs
What is the difference between feeling sad and having depression?
Sadness is a normal emotion that usually follows a stressor and improves with time. Depression lasts at least 2 weeks, affects daily functioning, and often includes changes in sleep, appetite, energy, concentration, or thoughts of worthlessness. A person may also lose interest in activities they usually enjoy.
How is major depressive disorder diagnosed?
Major depressive disorder is diagnosed by a clinician using symptom history, functional impact, and safety assessment rather than a single lab test. DSM-5 diagnosis generally requires 5 or more symptoms during the same 2-week period, with at least one being depressed mood or loss of interest. Doctors also try to rule out bipolar disorder, substance effects, and medical causes such as thyroid disease.
Can depression cause physical symptoms?
Yes. Depression can cause fatigue, poor sleep, appetite or weight changes, body aches, slowed movement, agitation, headaches, and reduced concentration. In many people, especially in primary care, physical complaints may be more noticeable than sadness at first.
What treatments work for depression?
The main evidence-based treatments are psychotherapy, antidepressant medication, or both together. Cognitive behavioral therapy and interpersonal therapy are commonly used, and antidepressants often take several weeks to show clear benefit. Severe or treatment-resistant depression may require options such as electroconvulsive therapy or transcranial magnetic stimulation under specialist care.
When is depression an emergency?
Depression is an emergency if someone has suicidal thoughts, a suicide plan, self-harm behavior, psychotic symptoms, or cannot care for basic needs. These situations need urgent assessment the same day, and immediate danger requires emergency services. Past suicide attempts, substance intoxication, and severe hopelessness increase risk.