“A new study in the UK has cast doubt on the supposed link between cannabis use and 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 latest edition of the journal Schizophrenia Research.

Not as predicted

Frisher and colleagues compared the trends of cannabis use with general practitioner records of schizophrenia.

They argue if cannabis use does cause schizophrenia, then an increase in cannabis use should be followed by an increase in the incidence of schizophrenia.

According to the study, cannabis use in the UK 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% between 1990 and 2010.

But the researchers found no increase in the diagnosis of schizophrenia or other psychotic disorders during that period. In fact some of the data suggested the incidence of these conditions had decreased.

“This study does not therefore support the specific causal link between cannabis use and the incidence of psychotic disorders,” the authors say”

http://www.abc.net.au/science/articles/2009/09/01/2673334.htm