Cannabis and schizophrenia. A longitudinal study of Swedish conscripts.
Level 3 - non-randomized controlled study
Prospective longitudinal cohort study with 15-year follow-up
PubMed 2892048 · doi:10.1016/s0140-6736(87)92620-1
What was done
A longitudinal cohort study evaluated the relationship between baseline cannabis consumption and the subsequent development of schizophrenia over a 15-year follow-up period in 45,570 Swedish military conscripts. Analysis adjusted for other psychiatric illness and social background.
What was found
High consumers of cannabis (use on more than 50 occasions) had a relative risk for schizophrenia of 6.0 (95% confidence interval 4.0 to 8.9) compared with non-users. The association remained after adjusting for other psychiatric illness and social background.
Why it matters
This study provides large-scale epidemiological evidence that heavy cannabis use in young adulthood is an independent risk factor for the subsequent development of schizophrenia.
Limits
The cohort consisted entirely of male military conscripts, limiting generalizability to women. Exposure was measured by self-report at baseline without tracking changes in cannabis use over the 15-year period, and residual confounding from unmeasured factors cannot be excluded.
Cited by
- supports Swedish military registry cohort studies found that men who used cannabis during their teenage years had higher rates of psychotic disorders in adulthood.