Title: Cannabis (ab)use in Psychosis: From Short- to Long-term Impact on Symptomatology
Substance use disorders, especially cannabis dependence, are common comorbid diagnoses among individuals suffering from psychotic disorders. While it is generally accepted that cannabis may worsen the outcomes of psychosis, the pathways through which this effect occurs are still unclear and debated. To date, there is some evidence showing that cannabis may exacerbate positive psychotic symptoms, cognitive impairment and medication side effects (Dekker, Linszen, & de Haan, 2009), but also some evidence supporting the presence of lower negative symptom scores in cannabis-dependent patients (Salyers & Mueser, 2001).
This talk will present results from an investigation into the effect on cannabis use on psychotic symptomatology, using novel network models (Borsboom & Cramer, 2013). We used data of patients diagnosed with a non-affective psychotic disorder from the longitudinal observational study Genetic Risk and Outcome of Psychosis Project (Korver et al., 2012) and included three measures of cannabis use: current cannabis use, intensity of cannabis use within the past year, and intensity of cannabis use within the past three years. Overall, our findings suggest that while on the short term there seems to be a negative association between cannabis use and negative symptomatology, the increased intensity of cannabis use leads to an increase in positive symptomatology, especially impacting on conceptual disorganization and paranoia, but also on the spectrum of general psychopathology symptomatology.