Pharmac knew for more than two weeks that three deaths had been linked to its epilepsy drug brand switch but didn't tell patients or the public.
The drug buying agency continued with the brand switch after being told on 29 October that three deaths had been reported over suspicions they were linked to the change.
Emails released under the Official Information Act also show the Pharmac board alerted Minister of Health David Clark to the deaths on 29 October, under the 'no surprises' policy, but he too said nothing publicly.
The medicines safety watchdog Medsafe also knew but only issued a safety notice on 12 November and it wasn't until 15 November that Pharmac backed down on the brand switch.
The Minster of Health told RNZ: "Any sudden death is a tragedy and my sympathies are with the family and friends. "These deaths are being investigated by the Coroner, and in the meantime PHARMAC has made changes to the way the brand change is being managed.
"There are clear and long-standing procedures for handling reports of possible harm caused by adverse reactions to medicines. It is not for Ministers to manage those processes, which are rightly a matter for clinical experts.
"That includes when, and how, these matters are made public."
Investigative reporter Guyon Espiner has the story.
