Cannabis use and the increased risk of psychosis: The debate continues

The scientific community have long debated the causal relationship between cannabis use and the risk factor for psychotic illnesses such as schizophrenia. Both sides of this controversial subject are put forward in two articles published today in F1000 Medicine Reports. To give rise to the debate, the authors of each article were given the opportunity to read the opposing side's article drafts and consider their arguments when structuring their own article.

In his article "Cannabis and psychosis: what causes what?" David Castle of the University of Melbourne argues for a causal link between cannabis use and an increased risk of psychotic symptoms. He does, however, concede that very few cases of schizophrenia would be prevented by a global abolition of cannabis, an argument put forward by Suzanne Gage, Stan Zammit and Matt Hickman of the Universities of Bristol and Cardiff in their article entitled "Stronger evidence is needed before accepting that cannabis plays an important role in the aetiology of schizophrenia in the population."

Gage et al argue that whilst acute psychotic experiences can be linked to cannabis use, the nature of the connection to schizophrenia inevitably remains much less certain. They argue that more robust evidence is required to determine whether preventing cannabis use will have any substantial impact on preventing psychotic disorders in the population, or within specific high-risk subgroups.

In their conclusions, both sides agree that cannabis is a public health concern and that the public should be made fully aware of the risks associated with using the drug. Castle states that this particularly applies to those who have a family history of schizophrenia or who have experienced psychosis-like symptoms, as they may be at greater risk.