Cannabis

Cannabis is the most commonly used illicit substance associated with psychosis and is a significant risk factor for the development of schizophrenia and substance-induced-psychosis.

Classification

Cannabis is a psychoactive substance derived from the Cannabis sativa plant. Its primary psychoactive component is delta-9-tetrahydrocannabinol (THC), which acts as a partial agonist at cannabinoid CB1 receptors in the brain.

Diseases Caused

Psychosis Risk

Cannabis use is associated with an increased risk of developing psychotic disorders:

• The relative risk (RR) of psychosis in cannabis users is approximately 2 compared to non-users.
• For heavy users, the risk increases to approximately sixfold.
• The association is strongest with high-potency cannabis (high THC content) and early-onset use.
• Cannabis use is also associated with an earlier age of onset of schizophrenia.

Substance-Induced Psychosis

Cannabis can acutely produce psychotic symptoms, particularly at high doses. These typically resolve as the drug is cleared, but can persist in vulnerable individuals.

📝 TODO: Needs source — cannabis dependence, withdrawal syndrome, cognitive effects, amotivational syndrome.

Diagnosis

• Diagnosis of cannabis-induced psychosis requires a temporal relationship between cannabis use and the onset of psychotic symptoms.
• Urine drug screening is part of the standard workup for first-episode psychosis.

Treatment

• Acute cannabis-induced psychosis is managed supportively; symptoms usually resolve with abstinence.
• Antipsychotics may be used for severe agitation.

📝 TODO: Needs source — specific treatment protocols, cannabis cessation strategies.

Exam Focus

Viva Questions

• What is the association between cannabis and psychosis? (RR 2; sixfold risk for heavy users.)
• How does this compare to other risk factors for schizophrenia? (Comparable to urban upbringing [RR 1.9] and migration [RR 2.9].)

MCQ Traps

• ⚠️ EXAM DETAIL: Cannabis is associated with a dose-dependent increase in psychosis risk — the risk is not simply present or absent.
• ⚠️ EXAM DETAIL: The association between cannabis and schizophrenia is strongest with high-potency cannabis and early-onset use.

Source Notes

• Information in this page is drawn from risk factor discussions in schizophrenia, which is sourced from the Shorter Oxford Textbook of Psychiatry and Dr. Ajith Jayasekara’s lectures.