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Condition

Depression: Signs, Causes, and Treatment

Depression (major depressive disorder) is a medical condition, not a character flaw, in which persistent low mood or loss of interest lasts two weeks or more and disrupts daily functioning. It affects roughly 8% of U.S. adults. Effective treatment — psychotherapy, antidepressants, or both — helps most people improve, though finding the right approach can take time.

Written by Gale Editorial · grounded in the cited clinical sources below · Updated 2026-06-15. How we write.

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What depression is — and is not

Depression is a medical condition, not a temporary mood or a sign of personal weakness. The clinical term is major depressive disorder (MDD), and it is defined by a specific pattern of symptoms that persist for at least two weeks and impair the ability to work, sleep, eat, or enjoy life 1.

Sadness is a normal human response to loss or disappointment. Depression is different: it is persistent, often disproportionate to circumstances, and does not lift with ordinary comfort or distraction. Roughly 8.3% of U.S. adults — an estimated 21 million people — experienced at least one major depressive episode in 2021 2. Depression is more common among young adults (18.6% of those aged 18–25) and among women (10.3%) compared to men (6.2%) 2.

Symptoms: the DSM-5 picture

Clinicians use the DSM-5-TR criteria established by the American Psychiatric Association: five or more of the following nine symptoms during the same two-week period, with at least one being depressed mood or loss of interest 1:

  • Depressed mood most of the day, nearly every day (feeling sad, empty, or hopeless)
  • Loss of interest or pleasure in activities once enjoyed (called anhedonia)
  • Significant change in appetite or body weight (increase or decrease)
  • Sleeping too much or too little (hypersomnia or insomnia)
  • Fatigue or loss of energy nearly every day
  • Feelings of worthlessness or excessive or inappropriate guilt
  • Difficulty thinking, concentrating, or making decisions
  • Psychomotor agitation or slowing (noticeable to others, not just subjectively felt)
  • Recurrent thoughts of death or suicidal ideation

To meet the threshold for MDD, symptoms must cause clinically significant distress or impairment in social or occupational functioning and must not be explained by a medical condition, substance use, or another mental disorder 1.

Depression also has physical dimensions that are frequently overlooked. Fatigue, sleep disruption, headaches, and digestive complaints are all reported by people with MDD — sometimes more prominently than the emotional symptoms.

Types of depression

Major depressive disorder is the most common form, but the depressive spectrum includes several distinct presentations 1:

  • Persistent depressive disorder (dysthymia) — chronic, lower-grade depression lasting at least two years
  • Postpartum depression — MDD beginning during pregnancy or within the first year after delivery; distinct from the "baby blues," which resolve within two weeks
  • Seasonal affective disorder (SAD) — depressive episodes tied to a seasonal pattern, typically emerging in autumn or winter
  • Treatment-resistant depression — MDD that has not responded to at least two adequate antidepressant trials
  • Depression with anxious distress — a DSM-5-TR specifier; anxiety and depression frequently co-occur and jointly shape treatment planning

Causes and risk factors

Depression does not have a single cause. The current evidence points to a convergence of genetic, neurobiological, psychological, and social factors 2:

  • Genetics — family history of depression meaningfully increases risk; heritability estimates suggest 30–40% genetic contribution
  • Brain chemistry and structure — neurotransmitter systems (serotonin, norepinephrine, dopamine) and structural differences in brain regions involved in mood regulation are consistently associated with MDD
  • Adverse life events — loss, trauma, abuse, chronic stress, and major life transitions are well-established precipitants
  • Medical illness — chronic pain, cardiovascular disease, thyroid conditions, and neurological disorders frequently co-occur with or trigger depression
  • Medication — certain drugs (corticosteroids, beta-blockers, some hormonal contraceptives) are associated with depressive symptoms as a side effect
  • Substance use — alcohol and many drugs of misuse are depressants; substance use disorders and MDD commonly co-occur

Age of onset peaks in the mid-20s, but depression can develop at any age.

Screening: the PHQ-9

The Patient Health Questionnaire-9 (PHQ-9) is the most widely used validated screening tool for depression in primary care. It asks how often each of the nine DSM-5 symptom domains has bothered the respondent over the past two weeks, on a scale of 0 to 3, yielding a total score of 0 to 27.

A meta-analysis of 29 studies (6,725 participants) found that a PHQ-9 cutoff score of 10 or above has a sensitivity of 0.88 and specificity of 0.85 for detecting MDD against a structured diagnostic interview 3. The PHQ-9 is a screening tool, not a diagnostic instrument — a positive screen indicates the need for a clinical evaluation, not a confirmed diagnosis.

The PHQ-9 is freely available and widely used by primary care clinicians, psychiatrists, and therapists to monitor treatment response over time.

Treatment: what the evidence supports

Depression is treatable. Across evidence-based options, the majority of people experience significant improvement — though finding the right approach can require time and adjustment 4.

Psychotherapy

Cognitive behavioral therapy (CBT) is the most studied psychotherapy for depression. A 2024 network meta-analysis of 676 randomized controlled trials (105,477 participants) found that combined individual CBT plus antidepressant medication was the most effective approach for more severe depression (SMD −1.18, 95% CrI −2.07 to −0.44), while CBT alone was effective for less severe presentations 4. Behavioral activation, mindfulness-based cognitive therapy, and problem-solving therapy also have meaningful evidence bases.

Antidepressant medications

For moderate-to-severe depression, second-generation antidepressants — SSRIs (such as sertraline, escitalopram) and SNRIs (such as venlafaxine, duloxetine) — are the recommended first-line pharmacologic options 5. In clinical practice, the number needed to treat (NNT) to achieve response or remission is approximately 6–7 for SSRIs and SNRIs, meaning a meaningful minority of patients do not respond to a given agent and may need a different drug or adjunctive treatment 5. Full antidepressant effect typically develops over 4–8 weeks; clinicians usually wait 6–8 weeks before concluding a trial is inadequate.

Combination and maintenance

Guidelines recommend a minimum of 6 months of treatment after achieving remission. For patients with three or more prior depressive episodes, long-term maintenance therapy significantly reduces recurrence risk. The ANTLER RCT (478 primary care patients followed for 52 weeks) found that patients who discontinued long-term antidepressants relapsed at more than twice the rate of those who continued (56% vs. 39%; hazard ratio 2.06) 6.

Other approaches

  • Lifestyle factors — regular aerobic exercise is associated with clinically meaningful symptom improvement and is supported as an adjunct in treatment guidelines
  • Esketamine (Spravato) — FDA-approved for treatment-resistant depression; administered in clinical settings under observation
  • Electroconvulsive therapy (ECT) — highly effective for severe or treatment-resistant MDD; modern ECT is performed under anesthesia and is far removed from its historical reputation
  • Transcranial magnetic stimulation (TMS) — an outpatient, non-invasive brain stimulation option for treatment-resistant cases

What to expect from the care process

A first appointment with a primary care clinician or behavioral health provider involves a structured conversation about symptom duration, severity, and impact on functioning. The clinician may administer the PHQ-9 and will rule out medical causes (thyroid dysfunction, anemia) with a brief exam or labs.

Getting an appointment is often the hardest step. Primary care can initiate an evaluation and prescribe antidepressants and also make referrals to psychiatry or therapy. Telehealth behavioral health visits are widely available and can reduce wait times substantially compared to in-person care.

A diagnosis of MDD requires clinical judgment — the clinician will assess whether the picture fits MDD or another condition (bipolar disorder, hypothyroidism, grief). Antidepressant response is gradual; clinicians typically re-evaluate 4–6 weeks into a new medication. Many people try more than one agent before finding the right fit — this is expected, not a failure.

Common questions

How is depression different from normal sadness?

Sadness is a normal response to difficult events and typically eases with time or comfort. Depression (major depressive disorder) is persistent — lasting at least two weeks — and includes a cluster of symptoms beyond mood, such as sleep disruption, appetite changes, loss of interest in activities, fatigue, and difficulty concentrating. Depression impairs functioning in ways that ordinary sadness does not, and it does not reliably lift without treatment.

What does the PHQ-9 score mean?

The PHQ-9 rates nine depression symptoms from 0 (not at all) to 3 (nearly every day). Total scores are generally interpreted as: 0–4 minimal, 5–9 mild, 10–14 moderate, 15–19 moderately severe, and 20–27 severe depression. A score of 10 or above is commonly used as a threshold to prompt further clinical evaluation. The PHQ-9 is a screening and monitoring tool, not a definitive diagnosis.

How long does depression treatment take to work?

Antidepressants typically require 4–8 weeks to reach full effect; some improvement in sleep or energy may be noticed earlier. Psychotherapy such as CBT is often delivered in 8–16 weekly sessions, with meaningful change typically seen by week 6–8. Combination treatment (medication plus therapy) may produce faster and more durable improvement than either alone, particularly for moderate-to-severe depression.

Can depression come back after treatment?

Yes. Depression has a tendency to recur: without maintenance treatment, relapse rates are substantially higher. The ANTLER trial found that primary care patients who discontinued long-term antidepressants relapsed at twice the rate of those who continued over 12 months (56% vs. 39%). For people with three or more prior episodes, guidelines recommend long-term or indefinite maintenance therapy. Mindfulness-based cognitive therapy (MBCT) is an evidence-based option to reduce relapse risk after remission.

Is depression the same as anxiety?

They are distinct conditions, though they frequently co-occur. Anxiety is characterized by excessive fear, worry, or dread about future events. Depression centers on persistent low mood, loss of interest, and hopelessness. The DSM-5 recognizes 'anxious distress' as a common specifier for MDD. When both are present, treatment typically addresses them together — CBT and SSRIs are effective for both conditions.

When does depression require urgent care?

If thoughts of death, self-harm, or suicide are present, reaching out to a crisis resource or emergency service is important. Call or text 988 (Suicide and Crisis Lifeline) to connect with a trained counselor. Go to the nearest emergency department or call 911 if there is immediate risk of harm. Depression with suicidal ideation is a medical emergency regardless of how certain the plan feels.

Related conditions

Condition/Anxiety

Specialties

Specialty/Behavioral Health · Specialty/Primary Care

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When to seek care

  • —Thoughts of suicide, self-harm, or death
  • —Inability to care for yourself or dependents
  • —Symptoms lasting more than two weeks that impair work, relationships, or daily tasks
  • —Sudden severe mood change, grandiosity, or days without sleep (may indicate bipolar disorder — requires a different treatment approach)
  • —Using alcohol or substances to manage mood
  • —New depressive symptoms in pregnancy or in the weeks after delivery

If you are having thoughts of suicide or self-harm, call or text 988 (Suicide and Crisis Lifeline) — available 24/7. For immediate danger, call 911 or go to the nearest emergency department.

General health information, not medical advice. Synthetic demonstration content.

References

  1. 1.American Psychiatric Association (2022). Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR): Major Depressive Disorder. American Psychiatric Association Publishing. link ✓DSM-5-TR diagnostic criteria for MDD: 9 symptom domains, 2-week duration, functional impairment threshold, exclusion criteria, and specifiers including anxious distress
  2. 2.National Institute of Mental Health (NIMH) (2023). Major Depression: Statistics. National Institute of Mental Health. link ✓Prevalence: 21.0 million U.S. adults (8.3%) had a major depressive episode in 2021; demographic breakdowns by sex (10.3% female, 6.2% male) and age (18.6% ages 18–25)
  3. 3.Levis B, Benedetti A, Thombs BD; DEPRESsion Screening Data (DEPRESSD) Collaboration (2019). Accuracy of Patient Health Questionnaire-9 (PHQ-9) for screening to detect major depression: individual participant data meta-analysis. BMJ. doi:10.1136/bmj.l1476 ✓PHQ-9 sensitivity 0.88 (95% CI 0.83–0.92) and specificity 0.85 (0.82–0.88) at cutoff ≥10 across 29 studies, 6,725 participants
  4. 4.Cipriani A, et al. (ECNP Depression Network Meta-Analysis Group) (2024). A systematic review and network meta-analysis of psychological, psychosocial, pharmacological, physical and combined treatments for adults with a new episode of depression. eClinicalMedicine (The Lancet). doi:10.1016/j.eclinm.2024.102780 ✓676 RCTs, 105,477 participants: combined CBT + antidepressants most effective for severe depression (SMD −1.18); CBT alone effective for less severe depression; antidepressants alone have minimal effect vs. placebo in mild depression
  5. 5.Kovich H, Kim W, Quaste AM (2023). Pharmacologic Treatment of Depression. American Family Physician. link ✓SSRIs and SNRIs recommended as first-line antidepressants; NNT of 7 for SSRIs and 6 for venlafaxine; escitalopram, mirtazapine, paroxetine, venlafaxine, amitriptyline show >50% symptom reduction at 8 weeks
  6. 6.Duffy L, Clarke CS, Lewis G, Marston L, et al. (2021). Antidepressant medication to prevent depression relapse in primary care: the ANTLER RCT. Health Technology Assessment. doi:10.3310/hta25690 ✓478 primary care patients: 56% relapse rate in discontinuation group vs. 39% in maintenance group at 52 weeks; hazard ratio 2.06 for relapse on stopping antidepressants

https://www.gale.care/conditions/depression · 6 sources. General health information, not medical advice — synthetic demonstration content.