"The lead researcher in the Christchurch study, Professor David Fergusson, said the role of cannabis in psychosis was not sufficient on its own to guide legislation. 'The result suggests heavy use can result in adverse side-effects,' he said. 'That can occur with ( heavy use of ) any substance. It can occur with milk.' Fergusson's research, released this month, concluded that heavy cannabis smokers were 1.5 times more likely to suffer symptoms of psychosis that non-users. The study was the latest in several reports based on a cohort of about 1000 people born in Christchurch over a four-month period in 1977. An effective way to deal with cannabis use would be to incrementally reduce penalties and carefully evaluate its impact, Fergusson said. 'Reduce the penalty, like a parking fine. You could then monitor ( the impact ) after five or six years. If it did not change, you might want to take another step.'
Bleakley, Louise, "NZ Study Used in UK Drug Review," The Press (Christchurch, New Zealand), March 22, 2005.