Educational Disclaimer: This case study is for educational and informational purposes only. It does not constitute medical advice, clinical guidance, or a substitute for professional psychiatric evaluation. All diagnostic criteria referenced are from the DSM-5-TR (APA, 2022). Clinicians should rely on their professional training, direct patient assessment, and current evidence-based guidelines when making diagnostic and treatment decisions.

Clinical Vignette

Patient: "Mr. G," 20-year-old college sophomore, brought to ED by roommate after he became paranoid, barricaded his dorm room, and claimed the CIA was monitoring him through his laptop camera.

Chief Concern: Roommate: "G ate a huge dose of THC edibles about 6 hours ago. He started freaking out 3 hours later — saying the walls were breathing, people were watching him, and the CIA had bugged his room."

History of Present Illness: Mr. G consumed a high-dose THC edible (estimated 100-150mg THC) approximately 6 hours before presentation. He has used cannabis recreationally for 2 years (smoking 2-3 times weekly) but has never consumed edibles at this dose before. Approximately 3 hours after ingestion, he developed: persecutory delusions (CIA monitoring him), referential delusions (TV anchors speaking directly to him), visual distortions (walls 'breathing'), auditory illusions (hearing whispered conversations), severe anxiety, and psychomotor agitation. He barricaded his dorm room and refused to open the door until his roommate called campus security. He has NO prior history of psychotic symptoms. He has NO family history of schizophrenia or psychotic disorders. His premorbid functioning was normal: maintained a 3.4 GPA, active social life, no behavioral concerns. Urine drug screen: THC positive. THC levels are expected to be elevated given the high-dose edible.

Medical History: No medical conditions. No prior psychiatric history.

Mental Status Exam: Agitated, scanning room, hiding behind stretcher. Tachycardic (HR 110). Pupils mildly dilated. Conjunctival injection. Speech pressured. Mood 'terrified.' Affect fearful, paranoid. Persecutory delusions present ('they're listening'). Visual distortions (walls moving). Oriented to person and place, disoriented to time. No formal thought disorder. Insight absent during episode.

Step 1: Substance-Induced Psychotic Disorder DSM-5-TR Criteria

Criterion A: Presence of prominent hallucinations or delusions.

Persecutory delusions (CIA monitoring). Referential delusions (TV speaking to him). Visual distortions (walls breathing). Auditory illusions (whispered conversations). MET.

Criterion B: Evidence from history, physical, or lab that symptoms developed during or soon after substance intoxication or withdrawal.

Symptoms began 3 hours after high-dose THC edible ingestion (consistent with edible onset). THC positive on UDS. No prior psychotic symptoms. MET — clear temporal relationship.

Criterion C: Not better explained by a primary psychotic disorder.

No prior psychotic symptoms. No prodromal symptoms. No family history of psychosis. Normal premorbid functioning. Symptoms emerged exclusively in the context of high-dose THC. MET.

Criterion D: Does not occur exclusively during delirium.

Mr. G is oriented to person and place (partial orientation). Not meeting full delirium criteria — disturbance is primarily psychotic, not confused. MET.

Criterion E: Significant distress or impairment.

Barricaded room. Required emergency services. Significant distress. MET.

Step 2: Cannabis-Induced vs. Primary Psychosis

Distinguishing whether cannabis CAUSED the psychosis or UNMASKED an underlying vulnerability is critical for prognosis:

Feature Cannabis-INDUCED Psychosis Primary Psychosis Triggered by Cannabis This Patient
Prior psychotic symptoms None Prodromal features may be identifiable retrospectively None identified
Temporal relationship Symptoms emerge during/shortly after use Symptoms persist weeks after cannabis clearance Emerged 3 hours after use — temporal fit
Resolution Resolves with substance clearance (hours-days) Persists beyond substance clearance PENDING: monitoring required
Family history Absent for psychotic disorders Often positive Absent
Premorbid function Normal May show decline Normal (3.4 GPA, social)
Dose relationship High-dose or novel exposure May occur at any dose Very high-dose edible (first time)

Critical Monitoring Window

Current evidence supports cannabis-INDUCED psychosis: clear temporal relationship, high-dose exposure, no prior symptoms, no family history, normal premorbid function. The DEFINITIVE test is resolution: if symptoms clear within 24-72 hours of last use, the diagnosis is confirmed as substance-induced. If symptoms persist beyond substance clearance, reassessment for primary psychotic disorder is mandatory.

Diagnostic Formulation

Diagnostic Conclusion

Cannabis-Induced Psychotic Disorder, with Onset During Intoxication (F12.259): All 5 DSM-5-TR criteria met. Psychotic symptoms following high-dose THC edible with clear temporal causation. No prior psychotic symptoms or family history. Treatment: (1) Supportive care in low-stimulation environment. (2) Benzodiazepine for acute agitation (lorazepam 1-2mg PRN). (3) Antipsychotic only if symptoms do not resolve with supportive care. (4) Cannabis cessation counseling (cannabis-induced psychosis is a strong risk factor for future psychotic episodes). (5) Follow-up at 72 hours and 2 weeks to confirm resolution. If symptoms persist >1 week after last use, reclassify as primary psychotic disorder and initiate appropriate treatment.

Teaching Points

  • The temporal relationship between substance use and psychotic symptom onset is the primary diagnostic tool for distinguishing substance-induced from primary psychosis. In substance-induced psychosis, symptoms should emerge during or shortly after intoxication (or withdrawal) and resolve when the substance clears. Persistence beyond clearance suggests a primary psychotic disorder that was triggered or unmasked by the substance.
  • THC edibles have a delayed onset (1-3 hours) and prolonged duration (6-12 hours) compared to smoked cannabis (onset minutes, duration 2-3 hours). This pharmacokinetic profile explains why Mr. G's psychosis began 3 hours after ingestion and may persist for 12+ hours.
  • High-potency THC products increase the risk of cannabis-induced psychosis. The relationship is dose-dependent: higher THC concentration correlates with higher psychosis risk. Mr. G's estimated 100-150mg edible dose far exceeds common recreational doses (5-10mg).
  • Cannabis-induced psychosis is a RISK FACTOR for future primary psychotic disorders. Follow-up data show that a significant proportion of individuals with cannabis-induced psychosis will develop schizophrenia within 3 years. This makes cannabis cessation counseling and longitudinal monitoring essential components of the treatment plan.
  • Benzodiazepines are preferred over antipsychotics for acute management of cannabis-induced psychosis because the symptoms typically self-resolve with substance clearance. Antipsychotics should be reserved for cases where symptoms persist despite supportive care and benzodiazepine treatment.