The relationship between the level of exposure to stress factors and cannabis in recent onset psychosis.

BACKGROUND: There is a lack of studies investigating the dose-response effect of childhood trauma, recent events and cannabis use on recent psychosis. This study aims to determine the relationship between the level of exposure to stress factors and cannabis use with psychosis and to determine the combination effect among these factors in predicting a psychotic disorder. METHODS: 146 recent onset psychotic (ROP) patients and 61 healthy controls were included. Childhood trauma was evaluated using the childhood trauma questionnaire (CTQ) and recent events using the Holmes-Rahe social readjustment scale. The pattern of cannabis use was assessed by a detailed interview. A hierarchical multiple regression was run in order to determine both the cumulative and independent contribution of each factor in predicting a psychotic disorder. RESULTS: The highest levels of exposure to childhood trauma and cannabis were associated with psychosis while neither low nor high recent event exposure was associated. The combined effect of risk factors yielded a significant association with psychosis (×2 = 86.76, p < .001) explaining the 49% of its variation. ROP were more likely to be exposed to one, two or three environmental factors than HC. Exposed to two or all factors were 7.5-fold and 26.7-fold more likely to have a diagnosis of psychosis, respectively. CONCLUSIONS: Our study provides evidence for a cumulative and a dose-response effect of environmental factors on recent psychosis. Considering that cannabis use and stress are highly prevalent in the population with psychosis, investigations of their relationships are needed to implement targeted prevention and treatment strategies.