F19 — Mental and behavioural disorders due to multiple drug use and use of other psychoactive substances

What is this category?

F19 plays the same role for this block that F28/F29 play for F20-F29 and F09 plays for F00-F09: it exists to teach when the honest classification is genuinely different from picking whichever single substance seems most prominent. F19 is used specifically when the pattern of use chaotically involves multiple substances such that no single one clearly predominates, or when a substance is used but its specific identity cannot be determined.

Core diagnostic concept

The classification question F19 answers is not "has this person used several different substances at some point?" (which describes many people) but "is the actual pattern of use so genuinely mixed, indiscriminate, or unidentifiable that assigning it to one specific F1x category would misrepresent the case, rather than simply being more convenient?" If one substance clearly predominates even alongside occasional other use, the specific category for that predominant substance is still the more accurate and more useful classification.

Key diagnostic features

Genuinely chaotic or indiscriminate multiple-substance use

A pattern in which several substances are used interchangeably or in combination, without one clearly predominating, such that assigning a single specific substance category would misrepresent the actual pattern.

Unidentifiable substance

Used when a psychoactive substance is clearly involved but its specific identity genuinely cannot be determined from the information available.

One substance predominates despite some other use

The key contrast case: occasional or incidental use of additional substances alongside a clearly predominant one does not, by itself, justify F19 over the predominant substance's own specific category.

The full framework still applies

F19 uses the same ten-state four-character framework (intoxication, harmful use, dependence syndrome, withdrawal state, and so on) as every other category in this block, applied to the mixed or unidentified pattern rather than to one named substance.

How to weigh evidence

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

• supports A pattern of using whatever substances are available on a given occasion — sometimes a sedative, sometimes an opioid, sometimes alcohol — with no single substance clearly predominating over recent months.
• consistent not decisive The person has tried several different substances at different points in their life. A history of varied past use, without a genuinely chaotic current pattern, does not by itself justify F19 over a more specific category if one substance is now predominant.
• raises alternative Heavy, regular alcohol use with occasional cannabis use at social events — alcohol clearly predominates, so F10 (with its own harmful use/dependence assessment) is the more accurate classification, not F19.
• contradicts or weakens A clear, consistent primary substance identified, with only rare or trivial additional use.
• missing and necessary to ask Whether one substance actually predominates in the pattern of use, rather than simply listing every substance ever used.

Duration and course

Minimum duration: As with the other four-character states in this block, the specific state (dependence syndrome, harmful use, and so on) still requires its own usual threshold to be met — F19 changes which substance identity is coded, not the criteria for the clinical state itself.

Course: There is no distinctive course requirement unique to F19 beyond that of the four-character state being applied.

Included presentations

• A genuinely chaotic or indiscriminate pattern of multiple-substance use with no single substance predominating.
• Use of a psychoactive substance whose specific identity cannot be determined from the available information.
• Any of the shared four-character states (intoxication, dependence syndrome, withdrawal state, and so on) applied to such a mixed or unidentified pattern.

Exclusions and distinguishing presentations

Four-character subtypes (orientation)

F19's own core concept — when this category, rather than a specific substance code, is the honest answer — is the assessed content here; its four-character subtypes individually are taught for orientation only and are not separately assessed in this pilot.

F19.0 — Acute intoxication

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.1 — Harmful use

Applied to a mixed or unidentified substance pattern causing demonstrable harm. (taught for orientation only, not separately assessed in this pilot)

F19.2 — Dependence syndrome

The six-criteria cluster applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.3 — Withdrawal state

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.4 — Withdrawal state with delirium

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.5 — Psychotic disorder

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.6 — Amnesic syndrome

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.7 — Residual and late-onset psychotic disorder

Applied to a mixed or unidentified substance pattern. (taught for orientation only, not separately assessed in this pilot)

F19.8 — Other mental and behavioural disorders

A mixed or unidentified-substance presentation not fitting the other listed states. (taught for orientation only, not separately assessed in this pilot)

F19.9 — Unspecified mental and behavioural disorder

A mixed or unidentified-substance disturbance identified but without enough information to classify further. (taught for orientation only, not separately assessed in this pilot)

Common learner errors

• Common mistake: Applying F19 whenever more than one substance is mentioned

Worked example — a predominant substance versus a genuinely mixed pattern

A 30-year-old reports drinking heavily most days for the past year, meeting several dependence-syndrome criteria for alcohol, and separately mentions using cannabis "now and then" at parties a few times a year, with no reported difficulty controlling that occasional use and no cannabis-related harm.

1. Step 1 — Identify what predominates: heavy, near-daily alcohol use meeting several dependence criteria is clearly the dominant pattern.
2. Step 2 — Characterise the additional substance: occasional cannabis use a few times a year, with no control difficulty or harm reported, is incidental rather than a co-equal pattern.
3. Step 3 — Check whether the overall pattern is genuinely chaotic or indiscriminate: it is not — one substance (alcohol) clearly predominates, with a separate, much lighter pattern of occasional cannabis use alongside it.
4. Step 4 — Weigh against F19: applying F19 here would obscure the fact that alcohol dependence syndrome is the clinically significant, classifiable pattern.
5. Conclusion — This is best classified under F10 (dependence syndrome, given alcohol clearly predominates), not F19, because one substance's own specific category remains the more accurate and more clinically useful classification when it clearly predominates.

Interactive practice

• Type A Whatever was around that night Recognition / application · Foundation
• Type B Mostly alcohol, but he mentioned a few other things too Boundary / differential · 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.

1. Without looking back at the page, state the question that decides whether F19 or a specific substance category applies.

   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.

   I recalled this I need to review this

2. Name one situation, other than a chaotic mixed pattern, where F19 would be the honest answer.

   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.

   I recalled this I need to review this

3. Explain in one sentence why mentioning more than one substance in a case does not automatically mean F19 applies.

   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.

   I recalled this I need to review this

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.