Police have been urged to better monitor drunk detainees, remove suicide risks and train staff on restraint dangers following an independent review of deaths in police custody over a decade.
The Independent Police Conduct Authority has released its findings from a review of 27 deaths during arrest or detention between 2000 and 2010.
All but one of those who died were male, and about half were Maori.
Thirteen were affected by alcohol at the time of their arrest, and nine were affected by drugs, while three deaths were specifically drug-related, the report says.
Five were only in custody for detoxification, sparking a recommendation for police to work with the Ministry of Health and other organisations to establish detox centres or temporary shelters.
It also recommended clearer guidelines on checking and rousing detainees, especially those under the influence of alcohol or drugs.
The report says seven people died following the use of restraint during arrest, and the deaths of a further seven were caused by medical conditions.
Police should receive training that reinforces the dangers of restraining people in a prone position with their hands behind their back, and the risks of potential asphyxia or other restrain-related medical conditions, the IPCA said.
Fourteen of those who died had mental health issues, although only 10 deaths were suicides.
The report recommends changes to how detainees are searched and evaluated for risks, ensuring medical examinations are available if necessary, and removing all possible suicide risk points and CCTV blind spots.
IPCA chair Judge Sir David Carruthers says the purpose of the review was not to attribute blame, but to "learn useful lessons".
Assistant Commissioner Operations Nick Perry said 13 of the 20 IPCA recommendations had already been actioned, while the remaining seven required further work or consideration.
"While any death in custody is a tragedy, this needs to be put in perspective against the 1.3 million people that police have dealt with in custody over the 10-year period covered by the report," he said.