A large number of people detained by police are drunk or on drugs at the time of their arrest, a new report shows.
The New Zealand Arrestee Drug Use Monitoring report reveals a sharp rise in drug and alcohol use among alleged offenders over the last two years.
It showed 41 per cent of 828 people surveyed after their arrests in Whangarei, Auckland, Wellington and Christchurch last year had drunk alcohol - up from 36 per cent in 2010.
Whangarei and Auckland had the biggest jumps in alcohol consumption among alleged offenders, with increases of 10 and 7 per cent respectively among those surveyed.
The average number of alcoholic drinks detainees had consumed before their arrest rose from 12 to 16.
Police said 21 per cent of those surveyed had been using drugs, sometimes along with alcohol. That included about 5 per cent who had been using methamphetamine.
Assistant Commissioner Malcolm Burgess said the report revealed a "core group" of problem drug users who were coming into regular contact with police.
"Half of the detainees were using alcohol or at least one illegal drug at the time of their arrest. The detainees had been arrested an average of three times in the previous 12 months, with a small number arrested on numerous occasions," he said.
The report also noted a rise in the number of alleged offenders who had used drugs in the year before their arrest.
In central Auckland, the proportion of detainees who had used methamphetamine in the last year climbed from 29 per cent in 2010 to 38 per cent in 2011
There was evidence of an increase in the price and decline in the availability of methamphetamine in Christchurch.
It was not clear how much impact the Christchurch earthquakes had on the disruption in supply, police said.
Nearly 30 per cent of detainees had used ecstasy and 75 per cent had used cannabis in the year before their arrest.
Detainees who had consumed larger quantities of alcohol, frequently used cannabis and often used methamphetamine were more likely to have committed a property crime and sold drugs in the previous month.