[THS] Doubt cast on cannabis, schizophrenia link

[Peter Webster]

[Doubt cast??? I wonder what you need for total demolishment of an idiotic claim]

Source: CBC News

http://www.cbc.ca/health/story/2009/09/02/cannabis-schizophrenia.html

Doubt cast on cannabis, schizophrenia link
September 2 2009

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 point out that "although using cannabis is associated with a
greater risk of developing psychosis, there is also evidence of
increased cannabis use following psychosis onset."

**Not as predicted**

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

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.

"This study does not therefore support the specific causal link
between cannabis use and the incidence of psychotic disorders," the
authors say. "This concurs with other reports indicating that
increases in population cannabis use have not been followed by
increases in psychotic incidence."