Do cannabis and urbanicity co-participate in causing psychosis? Evidence from a 10-year follow-up cohort study
Rebecca Kuepper, Jim van Os, Roselind Lieb, H.-U. Wittchen, Cécile Henquet
Psychological Medicine October 1, 2011 DOI: 10.1017/s0033291711000511 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Observational cohort Longitudinal Peer reviewed |
|---|---|
| Sample size | 1,923 |
| Population | German adolescents and young adults aged 14-24 years at baseline from the Early Developmental Stages of Psychopathology cohort study |
| Duration | 10-year follow-up |
| Measures | Munich version of the Composite International Diagnostic Interview |
| Topics | Cannabis |
| Key findings | Cannabis use and urban upbringing interact: cannabis use increased the risk of incident psychotic symptoms by 6.8% in urban areas but showed no significant effect in rural areas, with a significant interaction (10.9% adjusted difference in risk). |
Abstract
BackgroundCannabis use is considered a component cause of psychotic illness, interacting with genetic and other environmental risk factors. Little is known, however, about these putative interactions. The present study investigated whether an urban environment plays a role in moderating the effects of adolescent cannabis use on psychosis risk.MethodProspective data (n=1923, aged 14–24 years at baseline) from the longitudinal population-based German Early Developmental Stages of Psychopathology cohort study were analysed. Urbanicity was assessed at baseline and defined as living in the city of Munich (1562 persons per km2; 4061 individuals per square mile) or in the rural surroundings (213 persons per km2; 553 individuals per square mile). Cannabis use and psychotic symptoms were assessed three times over a 10-year follow-up period using the Munich version of the Composite International Diagnostic Interview.ResultsAnalyses revealed a significant interaction between cannabis and urbanicity [10.9% adjusted difference in risk, 95% confidence interval (CI) 3.2–18.6, p=0.005]. The effect of cannabis use on follow-up incident psychotic symptoms was much stronger in individuals who grew up in an urban environment (adjusted risk difference 6.8%, 95% CI 1.0–12.5, p=0.021) compared with individuals from rural surroundings (adjusted risk difference −4.1%, 95% CI −9.8 to 1.6, p=0.159). The statistical interaction was compatible with substantial underlying biological synergism.ConclusionsExposure to environmental influences associated with urban upbringing may increase vulnerability to the psychotomimetic effects of cannabis use later in life.