Much research has been devoted to the links between cannabis use and psychosis and a team of researchers from Maastricht University in the Netherlands has added to the evidence to suggest that there is a link. The researchers studied 1,923 people who were aged between 14 and 24 at the start of the study. They were asked about their cannabis use and assessed for psychosis symptoms at the start of the study (T1), 3.5 years later (T2) and 8.4 years later (T3). The researchers found that people who hadn't used cannabis at the start of the study but who used it between T1 and T2 had nearly twice the risk of developing psychosis symptoms by the end of the study. If they carried on using cannabis between T2 and the end of the study their risk was 2.2 times greater. By the end of the study the incidence rate of psychosis symptoms was 14% in those who had smoked cannabis compared to only 8% in those who hadn't.
Kuepper, Rebecca ... [et al] - Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study British Medical Journal doi: 10.1136/bmj.d738