Schizophrenia and the Environment: Within-Person Analyses May be Required to Yield Evidence of Unconfounded and Causal Association—The Example of Cannabis and Psychosis
Schizophrenia bulletin March 8, 2021 J. van Os, L. Pries, M. Ten Have et al.
Using a within-person design that controls for fixed genetic and nongenetic confounders, data from two general population cohorts followed over about 10 years show that prior cannabis use is strongly associated with later attenuated psychotic experiences (adjusted odds ratio 7.03). In contrast, prior psychotic experiences were not associated with later cannabis use. The findings suggest a causal effect of cannabis on psychosis, but not the reverse.