Substance-induced psychosis — timeline, conversion and dual care (MEQ)

(i) Definition and discriminators. Substance/medication-induced psychotic disorder is characterised by delusions and/or hallucinations with a temporal relationship to intoxication, withdrawal or a culprit medication, not better explained by a primary psychotic disorder, not exclusively during delirium, and causing distress or impairment. Discriminators: delirium shows fluctuating attention and medical instability (absent here); primary psychosis with concurrent use is favoured by premorbid decline, family history, and psychosis persisting well beyond the expected substance window after abstinence. A positive UDS supports exposure but does not alone prove SIP.^[3]

(ii) Assessment and investigations. Rebuild timeline (potency, frequency, last use 18 hours ago, onset of psychosis), collateral from parents, MSE with documented examples, suicide/violence/vulnerability risk, capacity and legal status under local statute (principles only — no invented section numbers), and diagnose cannabis use disorder on a second axis if criteria met. Investigations: observations already reassuring; UDS known; before antipsychotic obtain BMI/weight, BP, glucose or HbA1c, lipids, FBC, U&E, LFT, ECG QTc; pregnancy test if applicable. Escalate imaging/organic tests only if red flags appear.^[3][4]

(iii) Acute management. Low-stimulus environment, de-escalation, medical observation. If agitation: consider lorazepam 1–2 mg oral with observation. For ongoing psychosis: example olanzapine 5–10 mg orally at night (or risperidone 1–2 mg daily, or aripiprazole 10 mg daily) after baselines; educate on sedation/metabolic risk or akathisia depending on agent; early senior review. Do not withhold antipsychotic solely because UDS is positive. Least restrictive setting that contains risk; involve family.^[4]

(iv) Conversion risk and dual follow-up. Name evidence: Starzer — overall ~32% of SIP convert to schizophrenia-spectrum or bipolar illness; cannabis SIP among the highest (~47%). Murrie meta-analysis — pooled transition to schizophrenia after SIP around one quarter, higher for cannabis/amphetamines. Therefore: structured dual-aware follow-up (community team or EIS), motivational cannabis cessation as secondary prevention, family psychoeducation, written early-warning plan, and individualised antipsychotic duration with supervised review rather than same-day "cured" discharge or automatic lifelong schizophrenia fatalism. Integrated concurrent care of psychosis and cannabis use disorder — not sequential abstinence-first exclusion.^[1][2][5]