Police and the coroner's office should have told the government about a spate of synthetic cannabis deaths much sooner, Associate Health Minister Peter Dunne says.
Mr Dunne said the first he knew about seven deaths linked to unidentified psychoactive substances this month was about an hour before police made the information public in a news release.
That number rose to eight yesterday when a man died after becoming ill from smoking synthetic cannabis.
Mr Dunne was satisfied with the detection work police were doing to track down who was selling and distributing the drugs, which can contain a range of different and sometimes unknown chemicals.
"I'm not satisfied, though, with the information that's being shared," Mr Dunne told Morning Report.
"That information had obviously been known to police and the coronial officials for some time. I don't think it's reasonable that the government wasn't made aware of that until virtually the last minute."
The government was now coordinating a response from police, district health boards and Ministry of Health officials - something that could have been done earlier with better communication, he said.
The drugs were not always synthetic cannabinoids, but a range of unidentified psychoactive substances with unknown risks and effects, Mr Dunne said.
"We need to get some testing to take place of these substances to determine their toxicity."
The Psychoactive Substances Act, passed in 2013, was meant to create a regime where manufacturers could submit psychoactive drugs for testing and approval.
That regime was not working as it should, with no products yet submitted, Mr Dunne said.
"Because of the [ban on] animal testing provision, sadly what's happened is what I said would happen at the time - we've driven this market underground."
He had asked officials last week - before learning of the deaths - to review the latest science to see if there were any new ways of testing the safety of such drugs without relying on animal testing.
Massey University drugs research Christopher Wilkins told Morning Report regulating synthetic cannabis would help, but legalising actual cannabis could go one better.
"If you go to places where they've got better, more legal access to cannabis, you just don't get synthetic cannabinoids, because the users tell us that they actually prefer natural cannabis."
Mr Dunne agreed that more liberal laws for natural cannabis could help.
"But there are two big problems in this issue - one's called National and one's called Labour," he said.
"Both the major parties have consistently ruled out any change in this area."