Psych CASC / OSCE · Addiction psychiatry — cannabis and psychosis
Explain cannabis and psychosis to parents — CASC communication station
MRCPsych/FRANZCP-style communication station: dual formulation, potency risk, parallel treatment, SIP conversion honesty, non-moralising cannabis counselling, vocational hope.
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Target exams
Station brief
Format. Communication station, approximately 7–10 minutes active time after reading. You are the psychiatry registrar in the early intervention / dual-diagnosis clinic. [1]
Candidate instructions. Explain the working dual diagnosis (psychosis plus cannabis use), discuss what is known about high-THC risk, outline medical checks and treatment (medication and psychosocial cannabis help), address CBD myths, discuss university, and explain why follow-up matters even if symptoms improve after stopping. Check understanding. The examiner plays both parents. [1][2]
Candidate scenario
Your patient, age 19, has a working diagnosis of first presentation of psychosis with heavy high-THC cannabis use since mid-teens. Medical exclusion is underway. You plan aripiprazole 10 mg daily and motivational support for cannabis cessation. Parents ask: "Did the weed cause this forever? Should we just make him stop and skip tablets? What about CBD oil from the shop? Must he quit university?" [1][3]
Marking domains
- Empathy, structure, agenda-setting; non-moralising tone
- Dual formulation in plain language (two problems, one plan)
- Accurate potency/frequency risk explanation without absolute fatalism
- Rationale for antipsychotic plus monitoring (e.g. akathisia)
- CUD help: motivational/CBT-style support, not lectures alone
- Honest SIP conversion / need for follow-up
- CBD framed as research adjunctive evidence, not retail cure
- Education/vocation hope; safety-net and check understanding [1][2][3][4]
Reveal assessor key
Open. Thank them; name the time; ask main worries first. [1]
Explain dual problem. "He has symptoms of psychosis — a break from shared reality, such as fixed false beliefs and hearing a voice commenting — and he has a heavy cannabis use pattern that can trigger and worsen those symptoms. We treat both together." [1]
Causation without fatalism. Daily high-THC use is linked to higher risk of psychotic disorders in research, especially when use starts in the teens. Not everyone who uses cannabis gets psychosis; other factors also matter. Stopping is one of the most helpful steps he can take. [1][3]
Why medication. Tablets reduce intensity of psychotic symptoms for many people while the brain settles; we do not wait for a perfect clean urine before treating clear psychosis. Aripiprazole is a common careful start; restlessness can occur; we monitor physical health. [3]
Follow-up honesty. Even when symptoms improve after stopping, some people later develop longer-term psychotic illness — so we arrange review rather than one-off discharge. [2]
CBD. Research has tested CBD as an add-on in schizophrenia in specialist trials; shop oils are not the same as trial medicine and do not replace standard care. [4]
University. May need temporary adjustment, not automatic abandonment; recovery includes roles and goals. [1]
Close. Summarise, invite questions, crisis contacts, written info, review plan, family early-warning signs including cannabis lapse. [2][3]
References
- [1]Di Forti M, Quattrone D, Freeman TP, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study Lancet Psychiatry, 2019.PMID 30902669
- [2]Starzer MSK, Nordentoft M, Hjorthøj C Rates and Predictors of Conversion to Schizophrenia or Bipolar Disorder Following Substance-Induced Psychosis Am J Psychiatry, 2018.PMID 29179576
- [3]Schoeler T, Petros N, Di Forti M, et al. Effects of continuation, frequency, and type of cannabis use on relapse in the first 2 years after onset of psychosis: an observational study Lancet Psychiatry, 2016.PMID 27567467
- [4]McGuire P, Robson P, Cubala WJ, et al. Cannabidiol (CBD) as an Adjunctive Therapy in Schizophrenia: A Multicenter Randomized Controlled Trial Am J Psychiatry, 2018.PMID 29241357