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Heroin Addiction and Related Clinical Problems: 2009, 11, 3 (pages: 29 - 34)

Cannabis and Premonitory Symptoms of Schizophrenia: What Is the Time Sequence?

Vernex N., Dagher G., Touzeau D.

Summary: Nowadays, cannabis is the most widely used illegal drug in France. Epidemiological studies have shown that in schizophrenic patients the risk of developing cannabis dependence is six times what it is in the general population. However, debates on the real chronology of the appearance of psychiatric disorders and addictive cannabis behaviour are ongoing. The aim of this article is to try to find out how best to interpret the association of cannabis and premonitory symptoms through a review of the literature. Some recent longitudinal studies suggest a potential role for pre-existing troubles, taking the view that cannabis would only aggravate them and turn them into schizophrenic symptoms. By contrast, other studies propose a causal linkage as well as a dose-effect relationship between cannabis consumption and the appearance of schizophrenia. Conclusion: The methodology of these studies limits the possibility of a reverse causality. In addition, it must be noted that some research teams excluded from their cohort subjects who presented psychiatric disorders at entrance. Cannabis appears to be a risk factor for psychotic disorders, because it interacts with a pre-existing vulnerability. Neuroimagery research will make it possible to clarify the common cerebral mechanisms of cannabis and schizophrenia.