Medical School · Year 3 · Psychiatry · includes a quiz and discussion video

Seminar 02: Depressive Disorders

Year 3: Psychiatry Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Diagnose major depressive disorder using DSM-5 criteria
2. Differentiate types of depressive disorders
3. Identify risk factors and comorbidities
4. Select appropriate treatment modalities
5. Monitor treatment response and side effects
6. Recognize treatment-resistant depression

Seminar Outline

I. Overview of Depression

Depressive disorders represent one of the most significant public health challenges worldwide, with major depressive disorder ranking as a leading cause of disability across the globe. The lifetime prevalence of major depression ranges from fifteen to twenty percent, meaning that approximately one in five individuals will experience a depressive episode during their lifetime. Women are affected at approximately twice the rate of men, a disparity that emerges at puberty and persists throughout the reproductive years. The peak age of onset occurs in the twenties and thirties, though depression can manifest at any age from childhood through late life.

The etiology of depression involves complex interactions among genetic, neurobiological, psychological, and social factors. Genetic studies demonstrate approximately forty percent heritability, indicating substantial but incomplete genetic contribution. First-degree relatives of individuals with depression have two to three times the risk of developing the disorder themselves. Neurobiological research has implicated dysregulation of serotonin, norepinephrine, and dopamine systems, along with abnormalities in the hypothalamic-pituitary-adrenal axis stress response system. More recent research highlights the role of neuroinflammation and reduced neuroplasticity, including decreased brain-derived neurotrophic factor.

Risk factors for depression span multiple domains and help identify individuals who may benefit from enhanced surveillance or preventive intervention. Prior depressive episodes represent the strongest predictor of future episodes, with each successive episode increasing the probability of recurrence. Family history of depression confers elevated risk through both genetic and environmental pathways. Childhood adversity, including abuse, neglect, and parental loss, significantly increases lifetime depression risk. Chronic medical conditions including cardiovascular disease, diabetes, and chronic pain frequently co-occur with depression in bidirectional relationships. Substance use disorders complicate both diagnosis and treatment.

The neurobiological understanding of depression has evolved substantially from the original monoamine hypothesis. While reduced serotonergic and noradrenergic activity contribute to depressive symptoms, the delayed onset of antidepressant efficacy despite rapid receptor effects indicates that downstream neuroadaptive changes mediate therapeutic effects. Current models emphasize altered connectivity between prefrontal cortical regions and limbic structures including the amygdala and hippocampus. Elevated inflammatory markers in subsets of depressed patients have led to investigation of anti-inflammatory approaches. Glutamate system dysfunction, particularly involving NMDA receptors, has emerged as a therapeutic target with the development of ketamine and esketamine.

<image>Panel A: A bar graph showing lifetime prevalence of depression across age groups and genders. Panel B: A diagram illustrating the multifactorial etiology of depression including genetic, neurobiological, psychological, and social contributions. Panel C: A flowchart depicting risk factors for depression organized by modifiable versus non-modifiable categories. Panel D: A schematic of neural circuits implicated in depression showing prefrontal-limbic connectivity.</image>

II. Diagnostic Criteria - Major Depressive Disorder

The DSM-5 diagnostic criteria for major depressive disorder require the presence of at least five symptoms during a two-week period, representing a change from previous functioning. At least one of the five symptoms must be either depressed mood or anhedonia, the loss of interest or pleasure in previously enjoyable activities. Depressed mood must be present most of the day, nearly every day, and may be characterized by sadness, emptiness, or hopelessness. Anhedonia similarly must be present most of the day, nearly every day. The symptoms must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

The SIG E CAPS mnemonic provides a useful framework for remembering the nine criterion symptoms of major depression. Sleep disturbance includes both insomnia and hypersomnia. Interest decrease refers to anhedonia. Guilt and feelings of worthlessness describe excessive or inappropriate self-blame and diminished self-worth. Energy decrease refers to fatigue or loss of energy nearly every day. Concentration difficulties include diminished ability to think, concentrate, or make decisions. Appetite changes encompass both decreased and increased appetite, often accompanied by unintentional weight change. Psychomotor changes include both retardation and agitation observable by others. Suicidal ideation includes recurrent thoughts of death, suicidal ideation with or without plan, or suicide attempt.

Specifiers in DSM-5 provide additional information that guides treatment selection and prognosis. The anxious distress specifier indicates prominent anxiety symptoms that may require specific treatment attention. Melancholic features describe a distinct quality of depressed mood with profound anhedonia, diurnal variation with mood worse in the morning, early morning awakening, marked psychomotor changes, and excessive guilt. Atypical features include mood reactivity, significant weight gain or increased appetite, hypersomnia, leaden paralysis, and interpersonal rejection sensitivity. Psychotic features indicate the presence of delusions or hallucinations, typically mood-congruent themes of guilt, worthlessness, or nihilism.

Severity ratings help communicate clinical status and guide treatment intensity. Mild depression involves few symptoms beyond the minimum required, mild distress, and minor functional impairment. Moderate depression involves symptom count and intensity between mild and severe. Severe depression involves substantially more symptoms than minimum, markedly distressing symptoms, and significant functional impairment. The presence of psychotic features automatically indicates severe depression. Depression with catatonic features describes motor abnormalities requiring specific treatment considerations. The peripartum onset specifier applies when depression occurs during pregnancy or within four weeks postpartum.

<image>Panel A: A checklist format display of DSM-5 criteria for major depressive disorder with duration and severity requirements. Panel B: A visual mnemonic for SIG E CAPS showing each symptom domain with representative examples. Panel C: A comparison chart of depression specifiers showing melancholic versus atypical features. Panel D: A severity rating scale showing symptom count, distress level, and functional impairment for each category.</image>

III. Other Depressive Disorders

Persistent depressive disorder, previously known as dysthymia, describes chronic depression lasting at least two years in adults or one year in children and adolescents. The symptom threshold is lower than major depression, requiring depressed mood plus two of six additional symptoms including appetite changes, sleep changes, low energy, low self-esteem, poor concentration, and hopelessness. The chronic nature distinguishes this condition, with individuals rarely experiencing more than two symptom-free months during the required duration. When criteria for major depressive disorder are met during persistent depressive disorder, the term double depression applies, and both diagnoses should be recorded.

Disruptive mood dysregulation disorder was introduced in DSM-5 to address concerns about overdiagnosis of pediatric bipolar disorder and inappropriate treatment with mood stabilizers. This diagnosis applies to children ages six to eighteen who exhibit severe temper outbursts grossly out of proportion to the situation, occurring three or more times per week on average. Between outbursts, the mood is persistently irritable or angry most of the day, nearly every day, observable by others. Symptoms must be present for at least twelve months without a period of three or more consecutive months without symptoms. The diagnosis requires presence in at least two settings with severity in at least one.

Premenstrual dysphoric disorder describes significant mood symptoms occurring in the luteal phase of the menstrual cycle and improving within days of menses onset. At least five symptoms must be present from a list including mood lability, irritability, depressed mood, anxiety, decreased interest, difficulty concentrating, fatigue, appetite changes, sleep disturbance, feeling overwhelmed, and physical symptoms. At least one symptom must be mood lability, irritability, depressed mood, or anxiety. Prospective daily ratings for at least two symptomatic cycles confirm the diagnosis. First-line treatment includes SSRIs, which may be taken continuously or during the luteal phase only.

Other depressive presentations include substance-induced depressive disorder, depressive disorder due to another medical condition, and adjustment disorder with depressed mood. Substance-induced depressive disorder requires prominent mood disturbance directly attributable to substance intoxication or withdrawal, with symptoms exceeding those expected from intoxication or withdrawal alone. Depressive disorder due to another medical condition requires evidence that the disturbance is the direct pathophysiological consequence of a medical condition such as hypothyroidism, stroke, or Parkinson disease. Adjustment disorder with depressed mood describes depressive symptoms developing within three months of an identifiable stressor and resolving within six months of the stressor ending.

<image>Panel A: A timeline comparison showing persistent depressive disorder versus major depressive episode duration requirements. Panel B: A diagnostic flowchart for disruptive mood dysregulation disorder showing age, symptom, and setting requirements. Panel C: A calendar-based illustration of premenstrual dysphoric disorder symptom timing across the menstrual cycle. Panel D: A decision tree for differentiating primary depression from substance-induced and medical condition-related depression.</image>

IV. Clinical Presentation

Cognitive symptoms of depression significantly impact daily functioning and quality of life. Concentration difficulties manifest as trouble focusing on tasks, following conversations, or reading. Memory complaints often involve difficulty registering new information due to poor attention rather than true memory impairment. Indecisiveness may affect minor daily choices and major life decisions alike. Rumination describes the tendency to dwell repeatedly on negative thoughts, contributing to mood worsening in a self-perpetuating cycle. Cognitive distortions characteristic of depression include catastrophizing, black-and-white thinking, overgeneralization, and negative filtering that selectively attends to negative information.

Physical symptoms frequently dominate the clinical presentation, particularly in primary care settings and among certain cultural groups. Sleep disturbance may manifest as initial insomnia with difficulty falling asleep, middle insomnia with frequent awakenings, or terminal insomnia with early morning awakening typically occurring two or more hours before desired wake time. Hypersomnia may also occur, particularly in atypical depression. Appetite changes commonly involve decreased appetite with unintentional weight loss, though increased appetite with weight gain characterizes atypical depression. Fatigue and decreased energy often present as the most bothersome symptoms. Psychomotor changes may be observed as slowed movement and speech or as restless agitation.

Behavioral symptoms of depression reflect diminished motivation and interest. Social withdrawal may progress from decreased social activity to near-complete isolation. Decreased activity extends beyond social domains to include work, hobbies, and self-care. Neglect of hygiene and grooming may become apparent, particularly in more severe depression. Crying episodes may occur frequently, or conversely, patients may report inability to cry despite feeling sad. Avoidance of responsibilities may lead to accumulating problems that further worsen mood. These behavioral changes often precede full syndrome development and may serve as early warning signs.

Depression with psychotic features occurs in approximately ten to fifteen percent of severe depressive episodes and requires specific treatment considerations. Hallucinations, when present, are typically auditory and may involve derogatory voices consistent with the depressed mood. Delusions are more common and typically mood-congruent, involving themes of guilt, deserving punishment, worthlessness, or nihilism such as believing one's organs are rotting or that one has committed unpardonable sins. Mood-incongruent psychotic features such as persecutory delusions unrelated to depressive themes confer worse prognosis. Treatment requires combination of antidepressant and antipsychotic medications or electroconvulsive therapy.

<image>Panel A: A diagram showing cognitive symptoms of depression including concentration, memory, and characteristic distortions. Panel B: An illustration of physical symptoms organized by system including sleep, appetite, energy, and psychomotor domains. Panel C: A progression timeline showing behavioral changes from early warning signs through severe depression. Panel D: A comparison of mood-congruent versus mood-incongruent psychotic features with treatment implications.</image>

V. Assessment and Screening

Screening tools enable efficient identification of depression in clinical settings and provide standardized measurement of symptom severity. The Patient Health Questionnaire-9 comprises nine items corresponding to the DSM diagnostic criteria, each rated from zero to three based on frequency over the past two weeks. Total scores range from zero to twenty-seven, with established cutoffs for minimal, mild, moderate, moderately severe, and severe depression. The PHQ-2 provides ultra-brief screening using only the two core symptoms of depressed mood and anhedonia. A positive PHQ-2 should prompt full PHQ-9 administration or clinical interview.

PHQ-9 scoring guides clinical decision-making regarding treatment intensity and follow-up. Scores of zero to four suggest minimal depression not typically requiring treatment. Scores of five to nine indicate mild depression that may benefit from watchful waiting, support, or psychotherapy. Scores of ten to fourteen suggest moderate depression warranting active treatment with psychotherapy, pharmacotherapy, or both. Scores of fifteen to nineteen indicate moderately severe depression requiring active treatment and close follow-up. Scores of twenty to twenty-seven reflect severe depression often requiring multiple treatment modalities and consideration of more intensive interventions.

Medical workup for depression serves to identify potentially reversible medical causes and establish baseline parameters before treatment. Complete blood count screens for anemia, which can present with fatigue mimicking depression. Thyroid-stimulating hormone identifies hypothyroidism, a common and treatable cause of depressive symptoms. Vitamin B12 and folate deficiencies can cause both depression and cognitive symptoms. Basic metabolic panel identifies electrolyte abnormalities and assesses renal function relevant to medication selection. Drug screening may reveal undisclosed substance use contributing to symptoms. Additional testing is guided by clinical suspicion for specific conditions.

Differential diagnosis requires consideration of multiple conditions that may present with or mimic depressive symptoms. Bipolar disorder must be ruled out through careful history of manic or hypomanic episodes, as antidepressant monotherapy may destabilize bipolar patients. Normal grief responses to significant losses share symptoms with depression but typically do not require treatment unless prolonged or complicated. Adjustment disorder involves depressive symptoms in clear temporal relationship to an identifiable stressor. Hypothyroidism and other endocrine disorders may present with depression as the primary complaint. Substance-induced mood disturbances require careful assessment of temporal relationships. Dementia may present with depression, and depression may cause cognitive symptoms resembling dementia.

<image>Panel A: The PHQ-9 questionnaire layout showing items, response options, and scoring interpretation. Panel B: A flowchart for using PHQ-2 as a screening gateway to full PHQ-9 assessment. Panel C: A laboratory workup panel showing recommended tests and the conditions each identifies. Panel D: A differential diagnosis algorithm for depressive presentations with distinguishing features for each condition.</image>

VI. Treatment Overview

Treatment selection for depression depends on symptom severity, patient preferences, treatment availability, and clinical context. For mild depression, watchful waiting with support, lifestyle modifications, or psychotherapy alone may be appropriate initial approaches. Moderate depression typically warrants either psychotherapy or pharmacotherapy, with combination treatment providing additional benefit. Severe depression usually requires pharmacotherapy, often combined with psychotherapy, and may require consideration of electroconvulsive therapy particularly when psychotic features are present or rapid response is critical. Hospitalization may be necessary when safety concerns exist or outpatient treatment has proven insufficient.

Treatment goals are conceptualized in phases with distinct objectives. The acute phase aims to achieve response, defined as at least fifty percent reduction in symptoms, and ultimately remission, defined as minimal or absent symptoms. The acute phase typically requires eight to twelve weeks. The continuation phase, lasting four to nine months after remission, aims to prevent relapse, which refers to return of symptoms during the same episode. The maintenance phase, often extending one year or longer, aims to prevent recurrence, which refers to a new episode after recovery. Individuals with history of multiple episodes, residual symptoms, or high-risk factors benefit from longer maintenance treatment.

Time to treatment response follows a characteristic pattern important for patient education and clinical monitoring. Initial effects, including side effects and sometimes modest symptom improvement, typically emerge within one to two weeks. Significant clinical improvement generally requires four to six weeks at therapeutic doses. Full response may take eight to twelve weeks. An adequate trial is defined as six to eight weeks at a therapeutic dose with documented adherence before concluding that a treatment has failed. Premature discontinuation or dose changes prevent accurate assessment of treatment efficacy.

Multiple factors influence treatment selection beyond severity considerations. Symptom profile may guide choices; for example, patients with prominent insomnia may benefit from more sedating medications, while those with fatigue may do better with activating agents. Prior treatment response, both in the patient and in first-degree relatives, provides valuable guidance. Side effect profiles must be matched to patient concerns; sexual dysfunction, weight gain, and sedation represent common considerations. Medical comorbidities influence medication selection through effects on specific conditions and through drug interaction potential. Patient preference significantly impacts treatment adherence and should be incorporated into shared decision-making.

<image>Panel A: A treatment selection algorithm organized by depression severity from mild through severe. Panel B: A timeline showing acute, continuation, and maintenance treatment phases with their goals. Panel C: A graph depicting typical time course of symptom improvement with treatment. Panel D: A decision matrix showing how patient factors including symptom profile, comorbidities, and preferences influence medication selection.</image>

VII. Antidepressant Medications

Selective serotonin reuptake inhibitors represent the first-line pharmacological treatment for depression due to their favorable efficacy and tolerability profile. The class includes sertraline, escitalopram, fluoxetine, paroxetine, and citalopram. Sertraline offers a good balance of efficacy and tolerability with relatively few drug interactions, making it an excellent first choice. Escitalopram, the active S-enantiomer of citalopram, demonstrates good tolerability and efficacy with a simple dosing regimen. Fluoxetine has a long half-life that reduces discontinuation symptoms but can complicate drug interactions. Paroxetine is more sedating but has more prominent discontinuation effects. Citalopram carries dose-dependent QTc prolongation risk requiring dose limits.

Serotonin-norepinephrine reuptake inhibitors offer an alternative first-line option with potential advantages for certain symptom profiles. Venlafaxine provides dose-dependent norepinephrine effects, with higher doses offering more dual action, but requires blood pressure monitoring. Duloxetine offers established efficacy for comorbid pain conditions including diabetic neuropathy and fibromyalgia but should be avoided in hepatic impairment. Desvenlafaxine, the active metabolite of venlafaxine, offers simpler pharmacokinetics with fewer drug interactions. SNRIs may be particularly useful when depression is accompanied by fatigue, chronic pain, or inadequate response to SSRIs.

Additional antidepressant classes provide options for patients who do not respond to or tolerate first-line agents. Bupropion works through norepinephrine and dopamine mechanisms, produces no sexual side effects, and may aid smoking cessation but is contraindicated in seizure disorders and eating disorders. Mirtazapine antagonizes alpha-2 adrenergic and serotonin 5-HT2 and 5-HT3 receptors, produces significant sedation and weight gain, and may be useful when poor appetite and insomnia are prominent. Tricyclic antidepressants including amitriptyline and nortriptyline remain effective but carry greater side effect burden and lethality in overdose. Monoamine oxidase inhibitors including phenelzine and tranylcypromine require dietary restrictions but may help treatment-resistant depression.

Common side effects of SSRI medications follow predictable patterns that inform patient education and management. Gastrointestinal effects including nausea, diarrhea, and dyspepsia typically emerge early and often resolve within one to two weeks; taking medication with food may help. Sexual dysfunction including decreased libido, delayed orgasm, and erectile dysfunction affects a substantial proportion of patients and may persist; management options include dose reduction, drug holidays, switching medications, or augmentation. Sleep disturbance may manifest as either insomnia or sedation depending on the specific agent and patient; adjusting the timing of administration may help. Weight changes may occur with long-term use. Serotonin syndrome represents a rare but serious risk when SSRIs are combined with other serotonergic agents.

<image>Panel A: A comparison chart of SSRI medications showing dosing, half-life, and distinguishing characteristics. Panel B: A diagram illustrating SNRI mechanism of action with dose-dependent norepinephrine effects. Panel C: A decision tree for selecting among alternative antidepressant classes based on patient characteristics. Panel D: A side effect management guide organized by symptom with corresponding interventions.</image>

VIII. Psychotherapy for Depression

Cognitive behavioral therapy represents one of the most thoroughly researched and effective psychotherapies for depression. The cognitive model underlying CBT posits that negative automatic thoughts contribute to and maintain depressive symptoms. Treatment typically spans twelve to twenty sessions and involves identifying and challenging cognitive distortions, developing more balanced thinking patterns, and behavioral activation to increase engagement in rewarding activities. CBT demonstrates efficacy comparable to medication for mild to moderate depression and may provide more durable benefits with lower relapse rates after treatment discontinuation. The structured, skill-building nature of CBT allows for adaptation to various formats including individual, group, and digital delivery.

Interpersonal therapy addresses depression through the lens of interpersonal relationships and social functioning. IPT identifies one or more of four problem areas as the focus of treatment: grief involving complicated bereavement, role disputes involving conflicts with significant others, role transitions involving major life changes, and interpersonal deficits involving chronic difficulties in relationships. Treatment typically spans twelve to sixteen sessions and emphasizes improving communication, expressing emotions, and developing more satisfying relationships. IPT has established efficacy for major depression and is particularly well-suited for depression occurring in the context of interpersonal difficulties or life transitions.

Behavioral activation focuses specifically on the behavioral component of depression, targeting the inactivity and withdrawal that both result from and perpetuate depressive symptoms. The treatment rationale posits that depression leads to reduced engagement in positively reinforcing activities, which further worsens mood in a self-perpetuating cycle. Treatment involves identifying values, scheduling activities aligned with values, monitoring mood in relation to activities, and systematically increasing engagement with rewarding activities. Behavioral activation may be delivered in relatively few sessions and has demonstrated efficacy comparable to full cognitive behavioral therapy for some patient populations.

Other psychotherapy approaches offer additional options for patients who do not respond to or prefer alternatives to standard CBT or IPT. Psychodynamic psychotherapy explores how unconscious conflicts and early life experiences contribute to current symptoms and may be particularly suited for patients interested in deeper self-understanding. Mindfulness-based cognitive therapy combines cognitive therapy techniques with mindfulness meditation practices and has demonstrated particular efficacy for preventing depressive relapse. Problem-solving therapy focuses on developing structured approaches to current life difficulties and may be delivered briefly in primary care settings. Group therapy formats offer the benefits of social support and normalization while increasing treatment accessibility.

<image>Panel A: A diagram of the cognitive model showing relationships among situations, thoughts, feelings, and behaviors. Panel B: A visual representation of the four IPT problem areas with characteristic presentations for each. Panel C: A flowchart illustrating the behavioral activation cycle from depression through withdrawal through reduced reinforcement. Panel D: A comparison of psychotherapy modalities showing session number, focus, and evidence base for each approach.</image>

IX. Treatment-Resistant Depression

Treatment-resistant depression is typically defined as failure to achieve adequate response despite two or more adequate antidepressant trials of different mechanisms. Before concluding that depression is truly treatment-resistant, clinicians must verify that previous trials were truly adequate in terms of dose, duration, and adherence. Pseudo-resistance may result from inadequate dosing, insufficient trial duration, poor adherence, unaddressed substance use, or unrecognized medical or psychiatric comorbidities. Diagnostic reassessment should consider whether bipolar disorder, psychotic features, or personality disorders may be complicating treatment response. Confirming the accuracy of the diagnosis and adequacy of previous treatment represents the essential first step.

Optimization strategies aim to maximize the potential of current or previous treatments. Dose optimization involves increasing medication to the maximum tolerated dose, as many patients receive subtherapeutic doses. Duration extension provides additional time for response, as some patients require longer than the typical six to eight weeks. Adherence enhancement through education, simplification of regimens, and addressing barriers to compliance may reveal that apparent resistance actually reflected inconsistent medication taking. Switching medications to a different agent within the same class or to a different class represents another optimization approach.

Augmentation strategies add a second agent to enhance the effects of an antidepressant that produced partial response. Lithium augmentation has the longest evidence base and may be particularly useful given lithium's antisuicidal effects. Atypical antipsychotic augmentation with aripiprazole, quetiapine, or olanzapine has FDA approval for treatment-resistant depression, though metabolic monitoring is required. Thyroid hormone augmentation with triiodothyronine may enhance antidepressant effects independent of thyroid status. Adding bupropion to an SSRI combines different mechanisms and may address residual symptoms including fatigue and sexual dysfunction. Buspirone augmentation may help particularly when anxiety is prominent.

Advanced treatments offer options for patients who have not responded to multiple standard interventions. Electroconvulsive therapy remains the most effective treatment for severe depression, with response rates of seventy to ninety percent, and is particularly indicated for depression with psychotic features, catatonia, or suicidality requiring rapid response. Transcranial magnetic stimulation uses magnetic pulses to stimulate prefrontal cortex and has FDA approval for treatment-resistant depression. Ketamine and esketamine provide rapid-acting relief through NMDA receptor antagonism, with intranasal esketamine FDA-approved for treatment-resistant depression with required administration at certified healthcare settings. Vagus nerve stimulation is approved for treatment-resistant depression not responding to four or more adequate trials.

<image>Panel A: A flowchart for evaluating apparent treatment resistance including verification of adequate trials. Panel B: A decision algorithm for optimization strategies including dose increase, duration extension, and switching. Panel C: A comparison of augmentation options showing mechanism, evidence level, and monitoring requirements. Panel D: A guide to advanced treatments including ECT, TMS, and ketamine with indications and response rates.</image>

X. Special Populations and Prognosis

Depression in older adults presents distinct challenges in recognition and management. Presentation may emphasize somatic symptoms, cognitive complaints, or irritability rather than classic sad mood, leading to underdiagnosis. Pseudodementia refers to cognitive impairment caused by depression that improves with treatment, though differentiating from true dementia requires careful assessment. Vascular depression associated with cerebrovascular disease and white matter changes may have distinct neurobiology. Treatment requires attention to pharmacokinetic changes with aging, increased sensitivity to side effects, drug interactions with commonly prescribed medications, and medical comorbidities. Starting doses should be lower with gradual titration, but therapeutic doses remain the goal. Suicide completion rates are higher in older adults, particularly older white men.

Depression during pregnancy and the postpartum period requires careful balancing of risks and benefits of treatment. Untreated depression during pregnancy carries its own risks including poor prenatal care, substance use, preterm birth, and low birth weight. Most SSRIs are considered relatively safe in pregnancy, with sertraline and escitalopram often preferred due to lower breast milk levels. Paroxetine should be avoided in the first trimester due to cardiac malformation concerns. Valproate is absolutely contraindicated due to neural tube defect risk. Breastfeeding is generally compatible with many antidepressants, with sertraline and paroxetine having the lowest breast milk levels. For severe depression, electroconvulsive therapy is safe and effective during pregnancy.

Depression frequently co-occurs with other medical and psychiatric conditions, complicating both diagnosis and treatment. Comorbid anxiety disorders occur in approximately half of depressed patients and may require specific treatment attention. Substance use disorders have bidirectional relationships with depression and must be addressed concurrently. Chronic pain and depression share neurobiological substrates and may respond to duloxetine or tricyclic antidepressants. Cardiovascular disease patients benefit from SSRIs, with sertraline having the most evidence for post-myocardial infarction depression. Diabetes requires attention to weight effects of antidepressants and may worsen with some medications.

Prognosis for depression varies considerably based on multiple factors. Initial response rates to antidepressant medication are approximately sixty to seventy percent, with remission rates of thirty to forty percent with first treatment. Cumulative remission rates increase with successive treatment trials, though each subsequent trial has lower probability of success. Recurrence risk increases with each episode: approximately fifty percent after one episode, seventy percent after two episodes, and ninety percent after three episodes. Predictors of poorer outcome include comorbid conditions, residual symptoms, chronicity, and severity. Maintenance treatment substantially reduces recurrence risk and is particularly important for patients with multiple episodes or high-risk factors.

<image>Panel A: A clinical features comparison showing depression presentation in older versus younger adults. Panel B: A decision framework for antidepressant use in pregnancy showing risk-benefit considerations for each medication class. Panel C: A diagram illustrating bidirectional relationships between depression and common comorbid conditions. Panel D: A graph showing cumulative remission rates across sequential treatment trials and factors affecting prognosis.</image>

Summary

• MDD requires at least five symptoms for at least two weeks, with at least one being depressed mood or anhedonia, causing significant distress or impairment
• SIG E CAPS mnemonic covers criterion symptoms: Sleep, Interest, Guilt, Energy, Concentration, Appetite, Psychomotor changes, Suicidal ideation
• Specifiers including melancholic, atypical, psychotic, and peripartum onset guide treatment selection and indicate prognosis
• SSRIs represent first-line pharmacotherapy with sertraline and escitalopram generally well-tolerated and effective
• Common SSRI side effects include GI upset, sexual dysfunction, and sleep changes; serotonin syndrome risk with serotonergic combinations
• CBT is as effective as medication for mild-moderate depression and may provide more durable benefits with lower relapse rates
• Treatment timeline requires four to six weeks for significant improvement; adequate trial is six to eight weeks at therapeutic dose
• Treatment-resistant depression defined as failure of two or more adequate trials; augmentation, ECT, and ketamine are options
• Elderly patients may present with somatic symptoms; pseudodementia describes reversible cognitive impairment from depression
• Recurrence risk is fifty percent after first episode, rising to ninety percent after three episodes; maintenance treatment reduces recurrence

Key Terms

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