What Is Depression?
Major depressive disorder (MDD), commonly called depression, is a serious medical condition that affects mood, thinking, behavior, and physical health. It goes well beyond ordinary sadness — it is a persistent alteration in brain function that compromises the person's ability to feel pleasure, sustain energy, and function in daily life.
Depression is the leading cause of disability worldwide, according to the World Health Organization. Despite this, it remains underdiagnosed and undertreated — fewer than half of those affected receive adequate treatment, especially in developing countries.
Recognizing depression as a medical illness — with neurobiologic, genetic, and environmental underpinnings — is essential to reduce stigma and allow people to seek the treatment they deserve. Nobody chooses to have depression, just as nobody chooses to have diabetes or hypertension.
Neurobiologic Disease
Depression involves measurable changes in neurotransmitters, brain inflammation, and structural changes in areas such as the hippocampus and prefrontal cortex.
Highly Treatable
With appropriate treatment, 70-80% of patients show significant improvement. The combination of psychotherapy and medication offers the best results.
Global Impact
More than 280 million people worldwide have depression. It is the leading cause of disability and contributes significantly to the global burden of disease.
Pathophysiology
Our understanding of depression has evolved well beyond the simple "serotonin imbalance" hypothesis. We now know depression involves a complex network of neurobiologic changes that include neurotransmitter dysfunction, neuroinflammation, alterations in neuroplasticity, and dysregulation of the stress axis.
Monoaminergic Hypothesis
Reduced availability of serotonin, norepinephrine, and dopamine in the synaptic clefts contributes to depressive symptoms. Serotonin regulates mood and anxiety; norepinephrine, energy and alertness; and dopamine, motivation and pleasure. Most antidepressants act by increasing the availability of these neurotransmitters.
Neuroinflammation
Patients with depression have elevated levels of pro-inflammatory cytokines (IL-6, TNF-alpha, CRP) in the blood and cerebrospinal fluid. This chronic, low-grade neuroinflammation compromises serotonin production, reduces neuroplasticity, and contributes to the fatigue and cognitive symptoms of depression.
Neuroplasticity and BDNF
BDNF (brain-derived neurotrophic factor) is reduced in depression. This results in decreased neuroplasticity — the brain's ability to form new connections and adapt. Neuroimaging studies show reduced hippocampal volume in patients with chronic untreated depression. Antidepressants and physical exercise increase BDNF levels.
Symptoms
Depression manifests heterogeneously — not all patients have the same symptoms. There are melancholic forms (with weight loss and insomnia), atypical forms (with hypersomnia and increased appetite), and mixed forms (with anxiety components). Recognizing this diversity is essential for diagnosis.
Symptoms of Major Depressive Disorder
- 01
Persistent depressed mood
Profound sadness, a sense of emptiness, or hopelessness most of the day, nearly every day. In adolescents, it may manifest as irritability.
- 02
Loss of interest or pleasure (anhedonia)
Marked decrease in interest in previously pleasurable activities — hobbies, socializing, sex. One of the most specific symptoms of depression.
- 03
Sleep disturbances
Insomnia (especially early-morning awakening at 3-4 a.m.) in melancholic depression; hypersomnia in atypical depression.
- 04
Appetite and weight changes
Loss of appetite and weight in the melancholic form; increased appetite (especially for carbohydrates) and weight gain in the atypical form.
- 05
Fatigue and loss of energy
Profound, persistent fatigue, even without exertion. Simple tasks such as bathing can feel exhausting.
- 06
Psychomotor retardation or agitation
Slowing of thought, speech, and movement; or restlessness and an inability to stay still.
- 07
Difficulty concentrating
Working memory deficit, difficulty making decisions, and "mental fog". May be confused with dementia in older adults ("pseudodementia").
- 08
Feelings of guilt or worthlessness
Excessive self-criticism, a sense of being a burden to others. In severe forms, it may take on delusional proportions.
- 09
Thoughts of death or suicide
May range from a passive wish to "not wake up" to active planning. Present to some degree in 60-70% of depressive episodes.
- 10
Physical symptoms
Chronic pain (headache, low back pain), gastrointestinal problems, lowered immunity. Depression frequently presents with somatic complaints.
Diagnosis
Depression is diagnosed clinically, based on DSM-5 criteria. The PHQ-9 (Patient Health Questionnaire-9) scale is widely used for screening and monitoring. Laboratory tests help to exclude organic causes of depressive symptoms.
🏥DSM-5 Criteria for Major Depressive Disorder
Fonte: American Psychiatric Association — DSM-5
Criterion A: 5 or more symptoms for 2+ weeks
At least 1 of the symptoms must be depressed mood or anhedonia- 1.Depressed mood most of the day, nearly every day
- 2.Loss of interest or pleasure (anhedonia)
- 3.Significant weight loss or gain without dieting
- 4.Insomnia or hypersomnia
- 5.Psychomotor agitation or retardation
- 6.Fatigue or loss of energy
- 7.Feelings of worthlessness or excessive guilt
- 8.Difficulty concentrating or indecisiveness
- 9.Recurrent thoughts of death or suicidal ideation
Additional Criteria
- 1.Symptoms cause significant distress or functional impairment
- 2.Episode is not attributable to a substance or medical condition
- 3.Not better explained by schizoaffective or psychotic disorder
- 4.No prior manic or hypomanic episode (excludes bipolar disorder)
TESTS TO EXCLUDE ORGANIC CAUSES
| TEST | CONDITION TO EXCLUDE | RELEVANCE |
|---|---|---|
| TSH | Hypothyroidism | Most common cause of organic depression — always order |
| CBC | Anemia | Anemia can cause fatigue and depressive symptoms |
| Vitamin B12 and folate | Vitamin deficiency | B12 deficiency causes depression and cognitive symptoms |
| Vitamin D | Vitamin D deficiency | Associated with depressive symptoms, especially in older adults |
| Glucose / HbA1c | Diabetes | Diabetes and depression have a bidirectional relationship |
| Calcium / PTH | Hypercalcemia / hyperparathyroidism | Rare but treatable cause of depression |
| Cortisol | Cushing's syndrome | Hypercortisolism causes depression and cognitive changes |
DIAGNÓSTICO DIFERENCIAL
Differential Diagnosis
Hypothyroidism
- Fatigue, slowing, weight gain
- Cold intolerance
- Dry skin
Testes Diagnósticos
- TSH
- Free T4
Bipolar Disorder (Depressive Phase)
- History of manic or hypomanic episodes
- Family history
- Intense hypersomnia
- Antidepressant without mood stabilizer in bipolar disorder may induce mania
Testes Diagnósticos
- Detailed clinical interview
- MDQ
Prolonged Grief
- Recent loss of a loved one
- Sadness focused on the loss
- Time course of evolution
Testes Diagnósticos
- Clinical evaluation
- Prolonged grief criteria
Persistent Depressive Disorder (Dysthymia)
- Duration > 2 years
- Fewer simultaneous symptoms
- "I have always felt this way"
Testes Diagnósticos
- DSM-5 criteria
- Clinical interview
Anemia
- Fatigue, pallor
- Dyspnea on exertion
- Abnormal CBC
Testes Diagnósticos
- Complete blood count
- Ferritin
- B12
Hypothyroidism and Anemia
Organic causes of depressed mood must be ruled out before diagnosing major depression. Hypothyroidism is the main mimic: profound fatigue, psychomotor slowing, weight gain, cold intolerance, dry skin, and constipation — symptoms that completely overlap the depressive picture. TSH is mandatory in the initial workup. Well-treated hypothyroidism often resolves the depressive picture without antidepressants.
Anemia — especially iron-deficiency or B12-deficiency — also causes fatigue, apathy, difficulty concentrating, and irritability. Complete blood count with ferritin and B12 are basic tests. B12 deficiency in particular can cause significant neuropsychiatric changes, including depression, confusion, and neurologic symptoms. Adequate replacement resolves the symptoms without antidepressants.
Bipolar Disorder in the Depressive Phase
Distinguishing unipolar depression from bipolar disorder (BD) in the depressive phase is critical and often difficult. The depressive phase of BD is clinically identical to major depression — the difference lies in a history of manic or hypomanic episodes. Features that raise suspicion of bipolarity: intense hypersomnia, hyperphagia, recurrent episodes (3 or more), family history of BD, early-age onset, and inadequate response to multiple antidepressants.
The risk of diagnostic confusion is high: antidepressants without a mood stabilizer in bipolar patients can precipitate a manic switch, rapid cycling, or mixed states. The MDQ (Mood Disorder Questionnaire) helps with screening. When in doubt, refer for psychiatric evaluation before starting an antidepressant.
Prolonged Grief and Dysthymia
Grief is a normal human response to loss, but it can evolve into prolonged grief (PG) when it persists for more than 12 months with intense suffering and significant functional impairment. In PG, sadness focuses on the specific loss, with intense longing, difficulty accepting the death, and a sense that life has lost its meaning. In major depression, sadness is more diffuse and spans multiple domains of life.
Dysthymia (persistent depressive disorder) is a chronic, lower-intensity form of depression, lasting at least 2 years in adults. Patients often describe that "I have always been this way" — without recognizing that their chronic mood state is pathologic. Fewer simultaneous symptoms than in major depression, but cumulative suffering over the years is significant. Responds well to combined antidepressants and psychotherapy.
Treatment
Treatment of depression is multimodal. For mild depression, psychotherapy alone may suffice. For moderate to severe depression, combined psychotherapy and pharmacotherapy is recommended. Treatment choice should be individualized.
Psychotherapy
Cognitive-behavioral therapy (CBT) is the most studied psychotherapeutic treatment for depression. It identifies and modifies negative automatic thoughts and dysfunctional beliefs. Behavioral activation therapy, which focuses on resuming pleasurable and meaningful activities, is equally effective.
Interpersonal therapy (IPT) is another approach with strong evidence, focused on resolving interpersonal conflicts, role transitions, and grief that contribute to depression. Brief psychodynamic psychotherapy also demonstrates efficacy in clinical trials.
ANTIDEPRESSANTS: CLASSES AND CHARACTERISTICS
| CLASS | EXAMPLES | MECHANISM | SIDE-EFFECT PROFILE |
|---|---|---|---|
| SSRIs | Sertraline, Escitalopram, Fluoxetine | Inhibits serotonin reuptake | Nausea, sexual dysfunction, headache — generally well tolerated |
| SNRIs | Venlafaxine, Duloxetine, Desvenlafaxine | Inhibits serotonin and norepinephrine reuptake | Similar to SSRIs + sweating, hypertension at high doses |
| Atypical | Bupropion, Mirtazapine, Trazodone | Varied mechanisms | Bupropion: no sexual dysfunction; Mirtazapine: sedation, weight gain |
| Tricyclics | Amitriptyline, Nortriptyline, Clomipramine | Reuptake blockade of multiple monoamines | Sedation, dry mouth, constipation, weight gain, cardiac risk |
| MAOIs | Tranylcypromine, Phenelzine | Inhibits monoamine oxidase | Strict dietary restriction, risk of hypertensive crisis |
Weeks 1-2
Start antidepressant at a low dose. Psychoeducation about the illness. Suicide risk assessment. Sleep may improve before mood.
Weeks 3-4
Dose adjustment if needed. Antidepressant effects begin. Fatigue gradually lifts and cognition improves.
Weeks 6-8
Full therapeutic response expected. If response is inadequate, consider switching or augmentation.
Months 3-6
Continuation phase — maintain treatment to consolidate the response. Psychotherapy progresses.
6-12+ months
Maintenance phase. Duration depends on recurrence risk factors. First episode: minimum 6-9 months after remission.
Physical Exercise
Aerobic exercise has a clinically relevant antidepressant effect in mild to moderate depression, with magnitude described in some meta-analyses as comparable to that of medication. The mechanism includes increased BDNF, regulation of the HPA axis, release of endorphins, and reduction of inflammatory markers. The recommendation is 150 minutes per week of moderate activity.
Acupuncture as Treatment
Acupuncture has been studied as an adjuvant treatment for depression. Systematic reviews suggest acupuncture may be effective as a complement to antidepressants, enhancing therapeutic response and reducing medication side effects.
The proposed mechanisms — derived largely from preclinical and animal studies — include HPA-axis modulation, reduction of cortisol, increased availability of serotonin and norepinephrine, elevation of BDNF, and reduction of inflammatory cytokines. Neuroimaging studies show that acupuncture can normalize the activity of brain networks altered in depression.
Acupuncture is most often used as a complement, not a substitute, for conventional treatment. It can be particularly useful in patients with partial response to antidepressants, intolerance to medications, or preference for less pharmacologic approaches.
Prognosis
Depression is a highly treatable condition. With adequate treatment, 70-80% of patients achieve remission. However, depression has a recurrent nature: after the first episode, about 50% of patients will have another; after the third, the risk of recurrence rises to 90%.
Good prognostic factors include first episode, late onset, absence of psychiatric comorbidities, good social support, and early response to treatment. Maintaining treatment for an adequate duration is crucial to prevent relapse.
Untreated depression is associated with increased cardiovascular risk, diabetes, cognitive decline, and premature mortality. Adequate treatment not only relieves psychological suffering but also protects long-term physical health.
Myths and Facts
Myth vs. Fact
Depression is lack of willpower or 'weakness of character'.
Depression is a medical illness with a neurobiologic basis — it involves measurable changes in neurotransmitters, brain inflammation, and reduced hippocampal volume. Telling someone to 'cheer up' is as effective as telling someone with diabetes to 'normalize their glucose' through willpower.
Myth vs. Fact
Antidepressants change your personality and turn you into a 'zombie'.
Modern antidepressants (SSRIs, SNRIs) restore normal neurotransmitter function. The goal is for the patient to feel like themselves again before the depression — not to create an artificial personality. Anhedonia and apathy are symptoms of depression, not side effects of treatment.
Myth vs. Fact
If you have a 'good life', you cannot have depression.
Depression can affect anyone, regardless of external circumstances. Genetic factors account for 30-40% of risk. Some of the most successful and apparently 'happy' people suffer from severe depression — the condition does not discriminate by social class, achievement, or success.
When to Seek Help
If you or someone you know is experiencing symptoms of depression, seeking help is the most important step. Depression is treatable and recovery is possible.
Frequently Asked Questions About Depression
Major depression is a psychiatric disorder with neurobiologic underpinnings, marked by depressed mood or anhedonia (loss of pleasure) lasting at least 2 weeks, alongside symptoms such as changes in sleep, appetite, energy, concentration, and thoughts of death. It differs from ordinary sadness in duration, intensity, and significant functional impairment. Ordinary sadness is an adaptive response to adverse situations — depression persists even without an identifiable trigger.
Core symptoms are persistent depressed mood and/or anhedonia (loss of interest in previously pleasurable activities). Associated symptoms include sleep changes (insomnia or hypersomnia), appetite and weight changes, fatigue or loss of energy, observable psychomotor agitation or slowing, feelings of worthlessness or excessive guilt, difficulty concentrating, and recurrent thoughts of death or suicidal ideation. Diagnosis requires 5 or more symptoms for at least 2 weeks.
Diagnosis is clinical, based on DSM-5 criteria. The PHQ-9 scale is widely used to screen and monitor severity (mild 5-9, moderate 10-14, moderately severe 15-19, severe 20-27). Labs help exclude organic causes — mainly TSH (hypothyroidism), CBC (anemia), B12, and vitamin D. Ruling out bipolar disorder is essential before starting antidepressants.
For mild depression, psychotherapy (CBT) and physical exercise have efficacy comparable to antidepressants. For moderate to severe depression, combined pharmacotherapy and CBT offers the best results. First-line antidepressants are SSRIs (sertraline, escitalopram) and SNRIs (venlafaxine, duloxetine). Full response occurs in 4-8 weeks. Treatment should continue for at least 6-12 months after remission to prevent relapse.
Yes. Recent meta-analyses suggest acupuncture may be superior to placebo, with efficacy comparable in some studies to antidepressant medication for mild to moderate depression. The mechanism involves modulation of the serotonergic, dopaminergic, and noradrenergic systems, regulation of the HPA axis (cortisol), and stimulation of neurotrophic factors such as BDNF. Acupuncture is used as an adjuvant treatment, enhancing antidepressant response and improving associated symptoms such as insomnia and anxiety.
No. SSRIs and SNRIs — first-line medications — do not cause dependence in the pharmacologic sense (no tolerance, no drug-seeking behavior, no compulsion). Abrupt discontinuation may trigger discontinuation syndrome (dizziness, nausea, irritability, electric-shock sensations), which resolves with gradual tapering over weeks. This is not dependence — it is physiologic adaptation to the medication. The decision to stop should be made with the physician.
For a first depressive episode, treatment should continue for at least 6-12 months after complete remission to prevent relapse. For patients with 2 or more episodes, or with risk factors (severe episode, early onset, family history), maintenance treatment for 2-3 years or indefinitely may be recommended. The decision to discontinue should be shared with the physician and carried out with gradual tapering.
No. Sadness is a normal human emotion — an adaptive response to losses, frustrations, or difficult situations. It is proportional to the event, temporary, and does not impair functioning. Major depression is a neurobiologic disorder that persists regardless of external circumstances, causes intense suffering, impairs functioning, and does not respond to simply "wanting to feel better". Confusion between the two concepts contributes to stigma and delay in treatment.
Yes, the relationship is bidirectional and intense. Depression frequently presents with physical symptoms: diffuse muscle pain, headache, fatigue, gastrointestinal problems, and chest pain. This phenomenon is called depressive somatization. Conversely, chronic pain (low back pain, fibromyalgia, migraine) significantly increases the risk of depression. SNRIs such as duloxetine treat both depression and chronic pain. Acupuncture also addresses both simultaneously.
Seek help if: depressed mood or loss of pleasure persists for more than two weeks; there is significant impairment in work, relationships, or self-care; you have thoughts of death or that it would be better not to be alive — in that case, seek help immediately (in the United States, dial or text 988; outside the US, contact your local crisis helpline; or go to an emergency department). Do not wait for it to worsen before seeking care. Depression is highly treatable, and early treatment significantly improves prognosis.
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