Adolescent bullying, cannabis use and emerging psychotic experiences: a longitudinal general population study

Background. Using longitudinal and prospective measures of psychotic experiences during adolescence, we assessed the risk of developing psychosis in three groups showing low, increasing and elevated psychotic experiences associated with bullying by peers and cannabis use in a UK sample of adolescents. Method. Data were collected by self-report from 1098 adolescents (mean age 13.6 years; 60.9% boys) at five separate time points, equally separated by 6 months, across a 24-month period. General growth mixture modelling identified three distinct trajectories of adolescents reporting psychotic experiences : elevated, increasing and low. Results. Controlling for cannabis use, bullying by peers significantly predicted change in psychotic experiences between Time 2 and Time 5 in adolescents belonging to the increasing group. No effect was found for the elevated or low groups. Controlling for bullying, an earlier age of cannabis use and cannabis use more than twice significantly predicted change in psychotic experiences in adolescents belonging to the increasing group. Cannabis use at any age was significantly associated with subsequent change in psychotic experiences in the low group. Reverse causal associations were examined and there was no evidence for psychotic experiences at Time 1 predicting a subsequent change in cannabis use between Times 2 and 5 in any trajectory group. Conclusions. Bullying by peers and cannabis use are associated with adolescents' reports of increasing psychotic experiences over time. Further research into the longitudinal development of psychosis in adolescence and the associated risk factors would allow for early intervention programmes to be targeted more precisely.