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

Concept, in one sentence

F19 applies only when use is genuinely chaotic/indiscriminate across multiple substances with none predominating, or the substance cannot be identified — not whenever more than one substance is mentioned.

Decisive boundary cues

• One substance clearly predominates, others are incidental -> use that substance's own specific category, not F19.
• No single substance predominates in a genuinely mixed pattern -> F19 is the honest answer.
• Substance used but its identity cannot be determined -> F19 is the honest answer.

Duration/course cue

No distinctive course requirement unique to F19 beyond that of the four-character state being applied.

Nearest alternatives

F10

Common mistake

Applying F19 as soon as more than one substance is mentioned anywhere in a case, without checking whether one substance actually predominates.

Retrieval prompt — one-line memory anchor

What single question would you ask first about which substance, if any, predominates in this pattern of use?