Can we interrogate public databases to fill critical gaps in mental health epidemiology? Testing the association between cannabis and psychosis in the UK as an example.

The psychoactive properties of cannabis have been known forever. Since 1987, several prospective studies have suggested an increased risk of psychosis among cannabis users, with alternative explanations failing to account for such an effect. A cause-effect relationship has thus been implied. Further evidence has indicated that there is a dose-response relationship, and high-potency cannabis varieties confer the greatest risk of psychosis. As cannabis use has become more common over the last decades, one would expect a related increase in the number of schizophrenia cases. However, evidence in this regard remains equivocal for several reasons, including relying on databases that are not primarily designed to address such question and the issue that solid information regarding the incidence of schizophrenia is a relatively recent acquisition. Recent years have seen the development of online web publications, such as Google Trends and "Our World in Data", where data are explorable and interactable for tracking and comparing trends over specific periods and world regions. By using such databases, we believe that the question whether changes in cannabis use are associated with changes in schizophrenia rates can be answered, at least partly. Therefore, we tested these tools by evaluating trends in cannabis use and both cases and prevalence of schizophrenia in the United Kingdom, one of the countries where the incident rates for psychotic disorder have been suggested to be particularly increased by cannabis consumption. Crossing data from these tools revealed that interest in cannabis has been growing at the country level for over 10 years, with a parallel overlapping raise in psychosis cases and prevalence. Following up on this example, let us think of how many public health opportunities these public resources may offer. The question now is whether public health interventions for the benefit of the general population will follow suit.