of showing psychotic symptoms in individuals who declared to have ever used high-potency cannabis are about three times larger than in individuals who declared to have never used cannabis during their lifetime. The risk of showing psychotic symptoms is further elevated if high-potency cannabis is used daily (i.e., OR = 5.4; P = 0.002; Di Forti et al. 2015). About 9 % of those who initiate cannabis use progress to regular use and abuse (e.g., Volkow et al. 2014; Budney et al. 2007). Given the possible adverse effects on health and lifetime outcomes and given its possible role in triggering first-episode of psychosis, it is important to understand the causes of individual differences in the liability to initiate cannabis use.
