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Objective: To prospectively assess the relationship between cannabis use and psychotic experiences over time., Method: In a longitudinal design, young adults aged 18-27years (N=705) gave online information on cannabis use and completed the Community Assessment of Psychic Experiences (CAPE). These measures were repeated after an interval ranging from six months to five years., Results: A decrease in cannabis use was associated with a decrease in total psychotic experiences (β=-0.096, p=0.01) after adjustment for a range of potential confounders. An increase in cannabis use was associated with increased positive symptoms at follow-up (β=0.07, p=0.02), but was not significantly associated with increases in Negative and Depression symptom scores, nor with the total number of psychotic experiences., Conclusion: In the first study to the association of change in cannabis use and psychotic experiences over time in the general population, we found an association between changes in cannabis use and changes in the frequency of psychotic experiences. While this does not prove a causal relationship between cannabis use and psychosis, our findings are consistent with studies suggesting that cessation of cannabis use may be beneficial in terms of reducing psychotic experiences., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Background: Cannabis use is associated with increased risk for psychotic-like experiences (PLEs) and psychotic disorders. It remains unclear whether this relationship is causal or due to confounding., Method: A total of 1929 young adults aged 18-30 years participated in a nationwide internet-based survey in The Netherlands and gave information on demographics, substance use and parental psychiatric illness and completed the Community Assessment of Psychic Experiences (CAPE)., Results: Cigarette smoking and cannabis use were equally strongly associated with the frequency of PLEs in a fully adjusted model (β = 0.098 and 0.079 respectively, p < 0.05). Cannabis use was associated with distress from PLEs in a model adjusted for an elaborate set of confounders excluding smoking (β = 0.082, p < 0.05). However, when cigarette smoking was included in the model, cannabis use was not a significant predictor of distress from PLEs. Cigarette smoking remained associated with distress from PLEs in a fully adjusted model (β = 0.107, p < 0.001)., Conclusions: Smoking is an equally strong independent predictor of frequency of PLEs as monthly cannabis use. Our results suggest that the association between moderate cannabis use and PLEs is confounded by cigarette smoking.