Cannabis and psychosis: lessons from a 19th century national study of “Indian Hemp and Insanity



O. Ayonrinde

Background: In nineteenth-century British India, concern regarding large numbers of asylum patients with ‘Indian Hemp Insanity’ led to establishment of the Indian Hemp Drugs Commission. At the time, the cannabis plant was widely used in pharmacopeia and a source of government revenue. Tasked with determining the public and mental health risks of cannabis use, the Commission highlighted the status of medical and recreational 19th century cannabis research.

Methods: Historiographic review of the Indian Hemp Drugs Commission Report (1892).

Results: In 1892, heavy cannabis use was found to be associated with severe mental illness (7.3% of asylum patients; 12.6% of patients with a diagnoses). About two-thirds were children and young adults with higher relapse rates. Risk increased with early cannabis use and a family history of mental illness. Cannabis induced psychosis was thought to have a shorter trajectory and better prognosis however some patients progressed to an enduring psychotic illness. Different cannabis potency and modes of consumption had different effects. Occasional cannabis use was felt to have medicinal benefits for some.

Conclusion: This nineteenth-century study found a dose-related effect of cannabis on mental health, particularly psychotic symptoms in young people. Pathophysiological observations were consistent with contemporary knowledge. This systematic and detailed historical largely foreshadowed our current scientific evidence.

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