The Corrections Department has admitted it put security ahead of the safety of Otago prisoner Jai Davis when he died four years ago.
A coroner has released the findings of a major inquest late last year into the death.
Davis, 30, died while on remand in an isolation cell at the Otago Corrections Facility in February 2011.
Coroner David Crerar has confirmed he died from swallowing lethal quantities of diazepam and codeine pills from a bottle hidden in his rectum, but found he did not mean to kill himself.
Mr Crerar has endorsed recommendations made by the Corrections Department and its prison health services, from which he said many lessons have already been learned.
However, he called for two further investigations by the Health and Disability Commissioner and the Independent Police Conduct Authority.
He criticised the initial police investigation as cursory and slow, and said the failure to investigate Davis' death properly hindered his work.
Corrections Department chief custodial officer Neil Beales said it accepted it wrongly put security first.
Mr Beales said the department now dealt with drug concealment cases very differently, and sent all prisoners to hospital first.
The police said they accepted the criticism that their initial investigation of Davis' death was slow and cursory, because officers were not alert to the possibility of running a manslaughter inquiry.