Psych · Addiction psychiatry — cannabis and psychosis
Cannabis use and psychosis
Also known as Cannabis-induced psychosis · Marijuana psychosis · THC psychosis · Skunk and psychosis · High-potency cannabis · Cannabis use disorder and psychosis · Substance-induced psychotic disorder cannabis · Dual diagnosis cannabis · Cannabis FEP
Exam-exhaustive fellowship reference on the cannabis–psychosis interface: THC potency and dose–response, adolescent risk, substance-induced versus primary psychosis, conversion after SIP, CUD treatment, early intervention dual care, dual formulation, CBD evidence and regional guideline framing. FRANZCP-primary, globally tagged.
Practise this topic
On this page
Study tools
Your progress
Saved on this device.
Target exams
Red flags
- New psychosis with fever, fluctuating attention, seizure, dysautonomia or rapid cognitive decline — exclude delirium and encephalitis before locking a cannabis-only label
- Persistent psychosis days to weeks after last cannabis use with family history or premorbid decline — do not discharge as 'just cannabis' without follow-up and dual-diagnosis plan
- Active suicidal intent, command hallucinations, high violence risk, or child protection concern — same-day senior review and documented safety plan
- Synthetic cannabinoid exposure with severe agitation or medical instability — medical resuscitation takes priority
- Daily high-THC use in an adolescent with attenuated or frank psychotic symptoms — early intervention interface, not watchful neglect
- Do not withhold antipsychotics solely because the urine drug screen is cannabis-positive
Meet the patient
An 18-year-old apprentice arrives at 11pm with his mother. For eight months he has smoked high-potency cannabis nightly. For three weeks he has been certain that his foreman keeps a file on him and reads his messages.[6][13]
He is frightened rather than flat, has barely slept in a week, and stopped turning up to work on Monday. Last joint: yesterday evening. Urine screen positive for cannabis and nothing else. Observations normal.[12][19]
His mother offers the line you will hear a thousand times: "It's only weed." The resident writes cannabis-induced psychosis, discharge when settled. The examiner will not ask you whether cannabis is harmful. The examiner will ask: "Which layer is this, and what have you booked for the next five years?"[4][9]
References20ShowHide
- [1]Andréasson S, Allebeck P, Engström A, et al. Cannabis and schizophrenia. A longitudinal study of Swedish conscripts Lancet, 1987.PMID 2892048
- [2]Moore TH, Zammit S, Lingford-Hughes A, et al. Cannabis use and risk of psychotic or affective mental health outcomes: a systematic review Lancet, 2007.PMID 17662880
- [3]Arseneault L, Cannon M, Poulton R, et al. Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study BMJ, 2002.PMID 12446537
- [4]Arseneault L, Cannon M, Witton J, et al. Causal association between cannabis and psychosis: examination of the evidence Br J Psychiatry, 2004.PMID 14754822
- [5]Marconi A, Di Forti M, Lewis CM, et al. Meta-analysis of the Association Between the Level of Cannabis Use and Risk of Psychosis Schizophr Bull, 2016.PMID 26884547
- [6]Di Forti M, Marconi A, Carra E, et al. Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis: a case-control study Lancet Psychiatry, 2015.PMID 26359901
- [7]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
- [8]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
- [9]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
- [10]Niemi-Pynttäri JA, Sund R, Putkonen H, et al. Substance-induced psychoses converting into schizophrenia: a register-based study of 18,478 Finnish inpatient cases J Clin Psychiatry, 2013.PMID 23419236
- [11]Large M, Sharma S, Compton MT, et al. Cannabis use and earlier onset of psychosis: a systematic meta-analysis Arch Gen Psychiatry, 2011.PMID 21300939
- [12]Myles H, Myles N, Large M Cannabis use in first episode psychosis: Meta-analysis of prevalence, and the time course of initiation and continued use Aust N Z J Psychiatry, 2016.PMID 26286531
- [13]Petrilli K, Ofori S, Hines L, et al. Association of cannabis potency with mental ill health and addiction: a systematic review Lancet Psychiatry, 2022.PMID 35901795
- [14]Gates PJ, Sabioni P, Copeland J, et al. Psychosocial interventions for cannabis use disorder Cochrane Database Syst Rev, 2016.PMID 27149547
- [15]Connor JP, Stjepanović D, Budney AJ, et al. Clinical management of cannabis withdrawal Addiction, 2022.PMID 34791767
- [16]Gray KM, Carpenter MJ, Baker NL, et al. A double-blind randomized controlled trial of N-acetylcysteine in cannabis-dependent adolescents Am J Psychiatry, 2012.PMID 22706327
- [17]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
- [18]Vaucher J, Keating BJ, Lasserre AM, et al. Cannabis use and risk of schizophrenia: a Mendelian randomization study Mol Psychiatry, 2018.PMID 28115737
- [19]Hasan A, von Keller R, Friemel CM, et al. Cannabis use and psychosis: a review of reviews Eur Arch Psychiatry Clin Neurosci, 2020.PMID 31563981
- [20]Galletly C, Castle D, Dark F, et al. Royal Australian and New Zealand College of Psychiatrists clinical practice guidelines for the management of schizophrenia and related disorders Aust N Z J Psychiatry, 2016.PMID 27106681