Category: F10 F11 F12 F13 F14 F15 F16 F17 F18 F19
F16 — Mental and behavioural disorders due to use of hallucinogens: facilitator sheet
Teaching objective
Unlike most other categories in this block, marked perceptual alteration during hallucinogen intoxication is the expected primary effect of the substance, not itself evidence of a psychotic disorder. The classification question is therefore less "is perception altered?" (expected) and more "does the disturbance persist well beyond the expected intoxication period, recur without further use, or amount to a sustained delusional or hallucinatory picture beyond perceptual alteration?"
Choose material
Worked example · Case: The colours were part of the plan · Case: It came back, out of nowhere
Worked example
Show scenario
A 24-year-old used a hallucinogen once at a festival several months ago, experiencing visual distortions and altered time perception for a few hours that resolved as expected by the next morning. Since then, he has had two brief episodes — each lasting under a minute — of similar visual distortion appearing without warning while otherwise sober, with no further hallucinogen use in the interim. He finds these episodes unsettling but otherwise functions normally.
Reveal step 1
Step 1 — Check the original intoxication: the initial episode's perceptual alteration during use, resolving fully by the next morning, is a straightforward, expected acute intoxication (F16.0).
Reveal step 2
Step 2 — Check for further use: he confirms no further hallucinogen use since that single occasion.
Reveal step 3
Step 3 — Characterise the later episodes: brief, spontaneous recurrences of the same type of perceptual disturbance, occurring in the clear absence of further use.
Reveal step 4
Step 4 — Weigh against ongoing intoxication or a sustained psychotic disorder: because there has been no further use and the episodes are brief and self-limited rather than a sustained delusional or hallucinatory picture, this does not fit F16.5.
Reveal step 5
Conclusion — The later episodes are best classified as a residual and late-onset psychotic disorder (F16.7) — the classic "flashback" phenomenon — distinct from both the original intoxication and from an ongoing substance-induced psychotic disorder.
Comparison points
F16's intoxication state is distinguished from a hallucinogen-induced psychotic disorder by persistence and severity beyond expected perceptual alteration, and its residual/late-onset subtype is distinguished from ongoing intoxication by spontaneous recurrence in the clear absence of further use.
Discussion prompts
Prompt 1
Without looking back at the page, state why marked perceptual alteration during hallucinogen intoxication is not automatically evidence of a psychotic disorder.
Prompt 2
Name the feature that distinguishes a "flashback" (F16.7) from ongoing intoxication.
Prompt 3
Explain in one sentence why the presence or absence of further use matters for classifying a recurrence.
Summary
Perceptual alteration is hallucinogen intoxication's expected primary effect; a more sustained delusional/hallucinatory picture is a psychotic disorder, while brief spontaneous recurrences without further use are the residual/late-onset subtype ("flashbacks").