Doubt cast on cannabis, schizophrenia link

A British study has cast doubt on the supposed link between cannabis use and schizophrenia, but at least one Australian researcher says the study needs more evidence. Previous research has suggested cannabis use increases the risk of being diagnosed with either psychosis or schizophrenia. This latest study, led by Dr. Martin Frisher of Keele University, examined the records of 600,000 patients aged between 16 and 44, but failed to find a similar link. "An important limitation of many studies is that they have failed to distinguish the direction of association between cannabis use and psychosis," the authors write in the September edition of the journal Schizophrenia Research. [...] They argue that if cannabis use does cause schizophrenia, an increase in cannabis use should be followed by an increase in the incidence of schizophrenia. According to the study, cannabis use in the United Kingdom between 1972 and 2002 has increased four-fold in the general population, and 18-fold among under-18s. Based on the literature supporting the link, the authors argue that this should be followed by an increase in schizophrenia incidence of 29 per cent between 1990 and 2010. But the researchers found no increase in the rates of schizophrenia and psychosis diagnosis during that period. In fact, some of the data suggested the incidence of these conditions had decreased. More...