Cannabis and psychosis: revisiting a nineteenth century study of ‘Indian Hemp and Insanity’ in Colonial British India.

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. The exotic cannabis plant was widely used in pharmacopeia and a source of government revenue. The Commission was tasked with determining the public health risks of cannabis use, particularly mental illness. This analysis of the Commission report seeks to highlight the status of 1892 cannabis research and compare it with current evidence for medical and recreational cannabis use.

METHODS:

Detailed historiographic review of the Indian Hemp Drugs Commission Report (1892).

RESULTS:

In 1892, heavy cannabis use was considered to have been associated with severe mental illness (7.3% of asylum patients; 12.6% of patients with 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 psychosis was found to have a shorter trajectory and better prognosis than other mental illnesses in the asylums. Different cannabis potency and modes of consumption had different effects. Occasional cannabis use was felt to have medicinal benefits for some. Appendices provided symptoms and demographic characteristics of cannabis-induced mental illness.

CONCLUSION:

This important nineteenth-century study observed frequency and dose-related effects of cannabis on mental health, particularly psychotic symptoms in young people with a previous or hereditary risk of mental illness. Pathophysiological observations were consistent with current knowledge. As one of the most systematic and detailed studies of the effects of cannabis of the time it foreshadowed contemporary cannabis issues.