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New research suggests more young adults drive under the influence of cannabis than alcohol.
The latest paper from Otago University's long-running Christchurch Health and Development study found on average, drivers aged 25 drove 2 1/2 times more under the influence of cannabis than they did on alcohol.
The findings give additional ammunition to the Government's move to introduce drug-driving regulations.
"We're quite surprised by these results as we expected to find that drink-driving is more risky than driving under the influence of cannabis," says Professor David Fergusson, who led the study.
The study asked 936 drivers aged 25 about their frequency driving under the influence of cannabis or alcohol. While a similar proportion of the group reported driving under the influence of cannabis (21 per cent) or alcohol (27.2 per cent) per year, the frequency of driving under the influence of cannabis was far higher.
Those questioned reported driving under the influence of cannabis on an average of nine occasions between the ages of 21 and 25. The average rate for drink-driving was 3.52 times. And after adjusting for other factors, those driving while on cannabis on more than 20 occasions in a given year had 1.4 times more car accidents than those who did not. For alcohol, the results suggested only a small increased risk.
Professor Fergusson said the net effects were that for the group of young people studied, cannabis posed a greater risk than drink-driving.
He pointed out, however, that the accidents were relatively minor and for the most part did not involve injury, and as cannabis use was highest among young adults, the results of the study may only be specific to that age group.
Two social trends appeared to have influenced the results, he said.
"There have been major efforts from publicity, legislation and law enforcement to reduce the rates of drink-driving. In contrast, while rates of cannabis use have increased dramatically amongst young adults, there has been little effort to regulate driving under the influence of cannabis."
Under a proposed new law, police will put a suspected drugged driver through a roadside test of balance, co-ordination and eye-pupil response. A driver who fails this check will be given a blood test and a positive result will lead to a prosecution.
Police Minister Annette King hopes to have the compulsory tests in place next year.
