KEY POINTS:
A police survey of more than 900 people arrested shows almost three-quarters tested had at least one illegal drug in their system at the time.
A one-year pilot study involved voluntary interviews of those arrested in Whangarei, Henderson, Hamilton and Dunedin.
Interviewees provided 557 urine samples, of which 406 were found to contain at least one illegal substance, figures obtained by the Herald show.
Cannabis - known to stay in the body in detectable amounts longer than other drugs - was the most commonly detected illegal drug, turning up in 68.6 per cent of samples. Methamphetamine was detected in 12 per cent of samples. Alcohol was the most commonly used drug around the time of an interviewee's arrest, appearing in 37.2 per cent of cases.
The New Zealand Arrestee Drug Abuse Monitoring study - released early to the Herald following an Official Information Act request - is the first study of drug use among criminals.
It suggests New Zealanders tried drugs earlier than their Australian counterparts. New Zealanders first try cannabis at age 13, compared with 14 for Australians. New Zealanders are also likely to try heroin earlier. Kiwi males are trying the drug at 16 and Australians at 19.
Australians, however, are sampling hallucinogens at age 15 and methamphetamine-based drugs at 18 - earlier than Kiwis who try them at age 16 and 19 respectively.
A total of 965 people were interviewed after being arrested for offences including breaching bail (38.8 per cent), serious assault (10.1 per cent) and theft (8.8 per cent).
Of the 775 who said they used cannabis, a fifth said they did "all or most" of their driving under its influence. About a fifth (18.4 per cent) of the 343 who admitted using methamphetamine did most their driving while affected.
Cannabis and methamphetamine are used mostly by men, while 80 per cent of methamphetamine users - of both sexes - were of Maori descent.
Both drugs - like most other drugs in the survey - were purchased mainly from a private house or flat.
Acting police Assistant Commissioner for strategy and policy performance Paula Rose said one concerning factor in the findings was that those who admitted to being dependant on a drug (39 per cent), were already the more vulnerable members of society.
"That group that say, 'hey, we are dependant', is a group of people who don't live in their own homes, don't have reliable forms of income, they're a group of people who don't appear to have much light at the end of the tunnel and they're suffering adverse effects on their lives as a result."
National Drug Intelligence Bureau co-ordinator Mick Alexander said the study highlighted the need for earlier intervention and education in schools.
The survey results are due to be officially released later today, and police are considering including more centres in future studies.
The success of the study has seen its funding extended to 2010, at a total cost of $1.2 million.
