Cannabis and Psychosis in Youth: revisiting evidence from a 19th century population study

Poster A84, Monday, October 8, 11:30 am - 1:00 pm, Essex Ballroom

Oyedeji Ayonrinde1; 1Queen's University, Kingston, Ontario, Canada

In nineteenth-century India, cannabis (Indian hemp) was socially acceptable and a considerable source of revenue across the British Empire for pharmacopeia and recreational use. However, concern regarding large numbers of asylum patients with ‘Indian hemp insanity’ led to establishment of the Indian Hemp Drugs Commission. Tasked with determining the health risks of cannabis use, the Commission carried out a detailed population study including all Indian asylums in 1892. Method: Historiographic review of the Indian Hemp Drugs Commission Report against current knowledge. Results: In 1892, heavy cannabis use was associated with increased risk of psychotic symptoms and mental illness in 12.6% of diagnosed asylum patients (7.3% of all asylum patients). About two-thirds of cannabis-attributed presentations were children and young adults with also significantly higher relapse rates. Risk increased with early cannabis use and a family history of mental disorder. Cannabis-induced psychosis was initially noted to have a shorter trajectory and better prognosis, however longterm use was linked with poorer outcomes. Different cannabis preparations and strengths had different effects on users. Interestingly, infrequent cannabis use was felt to have some medicinal benefits. Conclusion: This nineteenth-century population study found a dose, frequency and duration related effect of cannabis use on mental health, particularly psychotic symptoms in young. Predating modern neuroscience and psychopharmacology this detailed systematic population study made similar observations to contemporary science, cautioning against cannabis use in youth and the importance of primary prevention involving reducing access, minimal use, and avoidance of high potency cannabis in the reduction of ‘Indian hemp insanity’.

Topic Area: First Episode Psychosis

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