Category · F20-F29 block

F23 — Acute and transient psychotic disorders

Terminology note: "Acute and transient" refers to onset and course, not to severity — an F23 episode can look every bit as dramatic and severe as an F20 episode while it is happening. The category exists precisely so that short, self-resolving episodes are not automatically labelled as the more chronic illness.

What is this category?

F23 groups psychotic disorders defined by their timeline: acute onset (developing within about two weeks, often within days) and a typically brief course, frequently following an identifiable stressful event, with full recovery common within a few months. The symptom content during the episode can closely resemble F20 (delusions, hallucinations, disorganised behaviour) or shift rapidly from day to day (a polymorphic picture); it is the speed of onset and expected brevity of course, not the symptom list, that defines this category.

Core diagnostic concept

The classification question F23 answers is: "has a psychotic picture developed acutely (within about two weeks) and is it expected to, or has it already begun to, resolve within a short window, rather than persisting as a sustained illness?" F23 asks about timeline and trajectory; it deliberately does not ask learners to wait indefinitely, but it does require enough timeline information to distinguish an acute, likely self-limiting episode from an evolving F20 presentation.

Key diagnostic features

Acute onset: A change from a non-psychotic to a clearly psychotic state develops within about two weeks, often within 48 hours — much faster than the more gradual or insidious onset sometimes seen in F20.
Polymorphic or rapidly shifting symptoms: Delusions, hallucinations, and perceptual disturbances that change in type and intensity from day to day, sometimes hour to hour, along with an unstable, intensely felt emotional state.
May resemble schizophrenia in content: Some presentations include the same characteristic symptoms used to describe F20 (e.g. thought echo, passivity experiences), but the acute onset and expected brief course still point to F23 rather than F20, at least initially.
Often follows an acute stressor: A stressful life event in the days or weeks before onset is common, though not required for the category to apply.
Brief expected course: Full recovery within a few months is common and expected; the category anticipates resolution, not a chronic course.
Perplexity and emotional turmoil: A bewildered, perplexed quality and intense emotional turbulence are often present, sometimes more prominent than any single fixed symptom.

How to weigh evidence

These learning labels are teaching aids, not official ICD-10 terminology (see Sources and Method).

supports Delusions and hallucinations that developed over three days, shifting in theme from day to day, one week after a sudden job loss.
consistent not decisive The content of the delusions closely resembles F20's typical themes (e.g. persecution, reference).
raises alternative The presentation has now continued, essentially unchanged, for five weeks.
contradicts or weakens A gradual, months-long insidious decline in functioning preceding the psychotic symptoms, rather than a sudden onset.
missing and necessary to ask How long the current episode has lasted so far, and whether it is still ongoing or has already resolved.

Diagnostic boundary

F23 is distinguished from F20 mainly by onset speed and expected course: F23 develops acutely (about two weeks or less) and is expected to resolve within a short window, while F20 requires characteristic symptoms present for most of the time over at least one month, often continuing well beyond. If an F23-type presentation persists beyond its expected window, the classification should be revisited and may shift toward F20. F23 is distinguished from F22 by both onset and breadth: F22 is a slow-building, narrow, persistent delusional system, while F23 is a fast-onset, often broader and more rapidly shifting picture. F23 is distinguished from a mood disorder with psychotic features (outside this block) by checking whether the psychotic symptoms are confined to, and explained by, a manic or depressive episode.

Full comparisons:

F20 vs F23 — F23 — Acute and transient psychotic disorders

Duration and course

Minimum duration: No minimum duration is required to consider F23 — onset within about two weeks is the key threshold, not a minimum length of illness.

Course: Expected course is brief, commonly discussed as resolving within one to three months depending on subtype, often with full return to the previous level of functioning. This is the opposite duration pattern from F20 and F22, which both require persistence rather than brevity.

Why this matters Because F23 is defined partly by an expected trajectory, a case may need to be classified provisionally, with an explicit note that the classification should be reassessed if the episode continues beyond the expected window — this is a case where 'insufficient information, reassess after further observation' can be the pedagogically correct answer rather than a sign of an incomplete case.

Included presentations

A rapidly shifting (polymorphic) psychotic picture with acute onset within about two weeks, often following a stressor, expected to resolve within a short window.
An acute psychotic episode with symptoms resembling F20 in content, but with acute onset and, so far, a brief course not yet meeting F20's duration.

Exclusions and distinguishing presentations

Exclusions and where they point instead
If this is true instead…	Consider	Why
Characteristic F20 symptoms persisting for most of the time over one month or longer, without resolving within the expected F23 window	F20	Once the duration threshold is exceeded, the classification should generally be revised toward F20 regardless of how the episode began.
A slow-building, narrow, single-theme delusional system developing gradually over months, without acute onset	F22	F22's gradual, persistent, narrow pattern is a different timeline and breadth from F23's acute, often broader presentation.
Psychotic symptoms confined to, and fully explained by, a manic or depressive episode	external capsule	Mood-congruent psychotic features occurring only within a mood episode point toward a mood disorder with psychotic features rather than F23.
A psychotic presentation clearly and fully explained by acute substance intoxication or withdrawal, or by a diagnosed organic condition	external capsule	Organic and substance-related causes should be checked and, where present, classified under the appropriate category rather than F23.

Four-character subtypes (orientation)

These four-character subtypes are shown for orientation only. This product does not teach or simulate four-character coding decisions; the category-level (three-character) reasoning above is the learning target.

F23.0 — Acute polymorphic psychotic disorder without symptoms of schizophrenia: Rapidly changing, varied delusions and hallucinations plus intense emotional turmoil, without any of F20's characteristic symptoms present long enough to qualify. (taught for orientation only, not separately assessed in this pilot)
F23.1 — Acute polymorphic psychotic disorder with symptoms of schizophrenia: The same polymorphic picture as F23.0, but with some characteristic F20-type symptoms also present for at least part of the episode. (taught for orientation only, not separately assessed in this pilot)
F23.2 — Acute schizophrenia-like psychotic disorder: A relatively stable (not rapidly shifting) psychotic picture that meets F20's symptom criteria but not yet its duration, developing acutely. (taught for orientation only, not separately assessed in this pilot)
F23.3 — Other acute predominantly delusional psychotic disorders: Relatively stable delusions or hallucinations as the main feature, of acute onset, not meeting F20's full criteria. (taught for orientation only, not separately assessed in this pilot)
F23.8 — Other acute and transient psychotic disorders: A residual subtype for acute psychotic presentations of two weeks or less that do not fit the more specific subtypes above. (taught for orientation only, not separately assessed in this pilot)
F23.9 — Acute and transient psychotic disorder, unspecified: Used when the disorder is confidently acute and transient in nature but insufficient detail is available to select a more specific subtype. (taught for orientation only, not separately assessed in this pilot)

External causes to check first

Categories in this block require that the disturbance is not better explained by another external cause listed below. These short capsules are reminders, not full teaching modules.

External cause capsule — Affective disorders with psychotic features

A reminder to check whether psychotic symptoms are confined to, and explained by, a manic or depressive episode, before applying F20 or F25.

What to check:

Whether psychotic symptoms (e.g. mood-congruent delusions of guilt or grandiosity) appear only during a clearly established manic or depressive episode and resolve as the mood episode resolves.
Whether mood symptoms clearly preceded the psychotic features, or vice versa.
Whether the delusional content is mood-congruent (fitting the prevailing mood, e.g. grandiose ideas during mania) rather than the more mood-neutral or bizarre content typical of F20.
Whether this pattern has recurred across more than one episode, which would raise consideration of F25 rather than a simple mood disorder with psychotic features.

The full F30-F39 category pages (F30, F31, F32, F33) themselves, which cover the severity-and-psychotic-features gradient for manic and depressive episodes in depth; this capsule is a focused reminder of the boundary against F20/F25, not a substitute for those pages.

External cause capsule — Substance- or medication-related presentations

A reminder that psychotic symptoms temporally linked to substance use, intoxication, withdrawal, or medication require consideration of a substance-induced explanation before an F20-F29 category is applied.

What to check:

Timing: did the psychotic symptoms begin during or shortly after intoxication or withdrawal from a psychoactive substance?
Type of substance: stimulants, cannabis, hallucinogens, alcohol withdrawal, and some prescribed medications (e.g. corticosteroids, certain dopaminergic agents) are recognised in general clinical teaching as capable of producing psychotic symptoms.
Course after the substance is stopped: substance-induced psychosis typically improves within days to a few weeks of abstinence, though this is not absolute.
Whether psychotic symptoms were present before any substance use began, which would argue against a purely substance-induced explanation.

A full teaching module on F10-F19 (substance-related disorders), which is on this product's expansion roadmap.

External cause capsule — Organic or medical causes

A reminder that F20-F29 categories require ruling out an organic brain condition before applying a primary psychiatric classification; this is not a full teaching module on organic mental disorders (see the F00-F09 block, planned).

What to check:

Onset in the context of a known neurological condition (e.g. epilepsy, stroke, brain tumour, autoimmune encephalitis) or a general medical illness affecting the brain.
New focal neurological signs, seizures, marked confusion, or fluctuating consciousness accompanying the psychotic features.
Age of onset outside the usual range for a first psychotic episode, especially later-life onset without a prior psychiatric history.
Rapid cognitive decline alongside psychotic symptoms.

A full organic-mental-disorder teaching module (F00-F09), which is outside this pilot's scope.

Common learner errors

Common mistake: Ignoring duration and course

Worked example — a fast-moving picture after a sudden stressor

Youssef, 34, was well until three days ago, shortly after unexpectedly losing his job. Since then he has expressed a rapidly changing set of beliefs — first that coworkers conspired against him, then, within the same day, that he has a special mission to warn the public about a disaster — alongside brief episodes of hearing voices that come and go. His mood swings between intense fear and elation within hours. He is bewildered and disoriented about what is happening to him. There is no history of similar episodes, no substance use, and no medical illness.

Step 1 — Check onset speed: the picture developed over three days, following a clear acute stressor — well within F23's acute-onset window.
Step 2 — Check symptom stability: the delusional content and mood are both shifting rapidly from hour to hour and day to day, a polymorphic pattern characteristic of F23 rather than F20's more stable picture.
Step 3 — Check duration so far: only three days have elapsed, far short of F20's one-month threshold.
Step 4 — Check for external causes: no substance use or medical illness is reported, and no mood episode independent of the psychotic features is described.
Conclusion — F23 is best supported at this stage: acute onset, rapidly shifting polymorphic picture, following a clear stressor, with the classification to be reassessed if the episode continues beyond the expected window.

Interactive practice

Type A Three days, a lost job, and a shifting picture Recognition / application · Foundation
Type B Acute, dramatic — and a substance history Boundary / differential · Boundary
Type C Three days in, severe but new Insufficient information · Developing
Type D Past the expected window Progressive revision · Transfer
Type E A frightening first episode Misconception correction · Foundation
Type F Sorting the evidence — fast onset, shifting picture Explanation and evidence selection · Boundary

Retrieval prompts

Try answering each of these from memory before revealing where to check. Nothing you think or type here is sent or saved anywhere.

What two timeline features most strongly support F23 over F20?

Reveal answer location

Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
Why might a case need to be classified provisionally, with a note to reassess later, rather than definitively at first presentation?

Reveal answer location

Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.
Explain why symptom severity alone cannot distinguish F23 from F20.

Reveal answer location

Check Duration and course, Diagnostic boundary, or the rapid revision card below — the cue you need is one of those, in this category's own already-authored wording.

These self-checks are a personal study aid only, visible to you on this page for this visit — they are not stored and do not affect your mastery dimensions.

Rapid revision card

F23: A psychotic episode with acute onset (about two weeks or less) and an expected brief course, often following a stressor, regardless of how severe or F20-like the symptoms look during the episode.

Decisive boundary cues:

Acute onset within about two weeks, rapidly shifting picture -> weighs toward F23 over F20.
Symptoms persisting essentially unchanged beyond one month -> weighs toward F20 over F23.
Slow-building, narrow, single-theme delusion developing over months -> weighs toward F22 over F23.

Duration/course: Onset speed (acute, ~2 weeks or less) plus an expected brief course are the defining features, not a minimum duration.

Nearest alternatives: F20, F22

Common mistake: Classifying a dramatic, severe first presentation as F20 immediately, before duration and course have had a chance to clarify whether it is actually F23.

Retrieval prompt: How quickly did this start, and how long is it expected to, or has it already begun to, resolve?

(or use your browser's print function) Open full-page printable revision view →

Related glossary terms

Psychosis

A general descriptive term for a mental state in which a person's grasp of reality is significantly disturbed — typically through delusions, hallucinations, or marked thought disorder. Psychosis is a feature that can occur across many different categories, not a diagnosis in itself.

Open full glossary entry →
Delusion

A fixed, false belief that is firmly held despite clear evidence to the contrary, and that is not accounted for by the person's cultural or religious background.

Open full glossary entry →
Hallucination

A perceptual experience (in any sensory modality) that occurs without an external stimulus but is experienced as real.

Open full glossary entry →

Source basis

WHO ICD-10 international classification structure and code/title (ICD-10 Browser, 2019 English release).

Original educational synthesis, informed by general published clinical-education understanding of ICD-10 F23 concepts; no verbatim CDDG or DCR text is reproduced.

Last reviewed: 2026-09-12. Full policy: Sources and Method.

Educational resource only. This page and its cases teach ICD-10 classification reasoning using fictional scenarios. It does not diagnose real people and should not be used to assess yourself or anyone else.

↑ Return to top