Depression is a mood disorder marked by a persistently low or depressed mood and/or loss of interest or pleasure (anhedonia) lasting most of the day, nearly every day, for at least two weeks, accompanied by changes in sleep, appetite, energy, concentration, and self-worth. It is distinguished from ordinary grief or situational sadness by its duration, severity, and functional impairment, and from bipolar disorder by the absence of manic or hypomanic episodes. The underlying mechanism involves dysregulation of monoamine neurotransmitters (serotonin, norepinephrine, dopamine), hypothalamic-pituitary-adrenal (HPA) axis dysfunction, and structural/functional changes in limbic and prefrontal circuitry.
Depression is always pathological in the clinical sense, though transient low mood is a normal physiological response to loss or stress (bereavement) and does not meet diagnostic threshold unless it persists or intensifies. Clinically relevant subtypes include single-episode major depressive disorder (F32.-), recurrent major depressive disorder (F33.-), persistent depressive disorder/dysthymia (F34.1), premenstrual dysphoric disorder (F32.81), and adjustment disorder with depressed mood (F43.21). It is most commonly confused with dysthymia, which is a lower-intensity but more chronic (2+ years) form, and with bipolar disorder, which requires screening for any history of mania/hypomania before a unipolar depression diagnosis can be confirmed.
The word entered English in the 1590s as depression (noun), used first in astronomy and geography (“a sinking down, a hollow”), borrowed from Old French depression, from Latin depressionem (“a pressing down”), from deprimere — literally “to press down.” The psychiatric/emotional sense (“a lowering of spirits, dejection”) is attested from the 1660s, and the specific clinical/medical use as a diagnosable mood disorder emerged in the early 20th century, formalized within the DSM system by the 1980s. The root premere (“to press”) connects depression to the entire -press- root family: compress (com- “together” + press → “to press together”), repress (re- “back” + press → “to press back, hold down”), and suppress (sub- “under” + press → “to press under, hold down”). The prefix de- is highly productive in medical terminology, appearing in dehydration, degeneration, dementia, and detoxification.
🔀 ALIASES / ALTERNATE TERMS
Depressive(adjective form — appears in “depressive episode,” “depressive disorder,” “depressive symptoms”)
Clinical depression / Major depression(lay and clinical synonym for major depressive disorder; commonly used interchangeably by patients and in progress notes)
Vascular depression(late-life depression associated with cerebrovascular disease; not separately coded — code underlying condition plus depressive disorder)
Depressive disorder due to another medical condition(secondary/etiologic form; coded F06.31, F06.32, or F06.34 depending on features, with the underlying medical condition coded first)
Bipolar depression(the depressive-phase episode within bipolar disorder; coded under F31.- rather than F32/F33)
🔗 RELATED TERMS
Mania/Hypomania — the opposite pole from depression on the mood spectrum; characterized by elevated, expansive, or irritable mood with increased energy, distinguishing unipolar depression from bipolar disorder when mania/hypomania is ever present.
Dysthymia — shares the -thymia root (“mood, emotion”); a chronic, lower-grade form of depressed mood rather than a disordered acute episode.
Persistent depressive disorder — the current DSM-5/ICD-10-CM term that consolidated chronic major depression and dysthymia; coded F34.1; distinguished from episodic MDD by duration criteria (2+ years in adults).
Anxiety disorder — frequently comorbid with depression (mixed anxiety-depressive presentations); describe overlap and note that when both are documented, both should be coded, as neither is a “code first” default for the other.
Anhedonia — the loss of interest or pleasure in previously enjoyable activities; a core diagnostic criterion and mechanism underlying the functional impairment seen in depression.
Neurovegetative symptoms — adjective/descriptive term for the physical manifestations (sleep, appetite, energy, psychomotor changes) that accompany and help confirm a depressive episode.
Monoamine hypothesis — the leading neurochemical mechanism proposing serotonin, norepinephrine, and dopamine dysregulation underlie both physiological mood regulation and pathological depression.
Major depressive disorder — the primary disease entity defined by this term; single episode (F32.0-F32.9, F32.A) or recurrent (F33.0-F33.9).
Persistent depressive disorder (dysthymia) — another clinical entity defined by chronicity of this term; F34.1.
Postpartum depression — another clinical entity defined by this term at a specific life-stage/anatomic-hormonal context; F53.0.
Adjustment disorder with depressed mood — another clinical entity in the stress-response specialty; F43.21, tied to an identifiable stressor.
PHQ-9 (Patient Health Questionnaire-9) — the primary standardized diagnostic/screening tool used to evaluate depression severity and monitor treatment response.
TMS therapy, subsequent delivery and management, per session
⚠️ Coding Note:F32.- (single episode) and F33.- (recurrent) require review of prior documented episodes before code selection — never default to F32.9 without confirming episode count in the chart, since recurrent depression is frequently undercoded as a single episode when history isn’t fully reviewed. Sequencing: when depression is documented as secondary to a known physiological condition (e.g., post-stroke, hypothyroidism, Parkinson’s), code the underlying condition first, then F06.31/F06.32. Watch for the documentation trigger phrases “feeling down,” “low mood,” “poor sleep and appetite,” or “not himself/herself lately” — these should prompt a physician query for a specific depressive disorder diagnosis rather than defaulting to a symptom code (R45.- series). Payer-specific consideration:Medicare and most commercial payers require severity specificity (mild/moderate/severe, with or without psychotic features) for behavioral health authorization and level-of-care determinations, so F32.9/F33.9 “unspecified” should be a last resort, not a default. For inpatient profee coding specifically, confirm whether the encounter documentation supports F32.A (nonspecific depressive symptoms) versus a fully criteria-met MDD diagnosis (F32.0-F32.5), as this distinction affects both accuracy and downstream risk adjustment.