The Mental Health Foundation says both the police and healthcare system need to act quickly to stop people with mental health problems dying in custody.
An IPCA report yesterday found heavily intoxicated man Sentry Taitoko, who died after hitting his head on concrete in a police cell more than 100 times, did not get the help he needed.
In a separate report the IPCA criticised police over the treatment of people detained in cells, in particular those who have mental health issues. It said, in some cases, they have acted unlawfully.
Chief executive of the Mental Health Foundation Judi Clements said a person suffering from a mental disorder should not be put in a police cell.
"We've got to find a way of getting our police service and our healthcare system working together so that we avoid putting people who may be already vulnerable into a place that is going to do them potentially more harm than good."
Meanwhile, The Howard League for Penal Reform said it doubted the report will stop people dying in police custody.
The league's patron Nigel Hampton said police should be forced to make changes to its procedures.
In a report in 2012, the authority made several recommendations including the establishment of detox centres for drunk detainees.
Mr Hampton said he suspected none of those recommendations had been implemented.