Cannabis use and violence: Is there a link?

Background: While several studies suggest that cannabis users are at increased risk of interpersonal violence, it is not clear to what extent the association is causal. Our paper aims to assess the association between cannabis use and violence by using a method that diminishes the risk of confounding. Methods: We analysed data on cannabis use and violent behaviour from the second (1994) and third (1999) waves of the Young in Norway Longitudinal Study (cumulative response rate: 68.1%, n = 2681). We applied fixed-effects modelling to estimate the association between these behaviours, implying that changes in the frequency of violence were regressed on changes in the frequency of cannabis use. The effects of time-invariant confounders were hence eliminated. In addition, we included two time-varying covariates. Results: The elasticity estimate implies that a 10% increase in cannabis use frequency is associated with a 0.4% increase in frequency of violence (p=.024). Conclusions: Analyses of panel data on Norwegian youths reveals a statistically significant association between cannabis use and violence.