The Chief Coroner has opened a joint inquiry into four deaths linked to the anti-epileptic medication Logem.
Judge Deborah Marshall said she had to open a joint inquiry because of the high public interest in these cases and the effect on people's wellbeing.
She will investigate the cause and circumstances of the deaths and see if they could have been prevented in any way.
Judge Marshall said the inquiry would look at whether the change in brand to Logem may have changed the seizure control and whether that contributed to the deaths.
Pharmac pulled funding from the Lamictal and Arrow brands of lamotrigine and was switching up to 11,000 people to the generic version, Logem, in a bid to save $30 million. However it reversed the decision last month after the first three deaths were reported.
MedSafe warned Pharmac against the switch, saying it posed significant safety issues, but advised the drug buying agency that if it went ahead, all patients should see a GP before switching and vulnerable patients should see a specialist.
Four deaths and 50 adverse reactions have been reported to the Centre for Adverse Reactions Monitoring over suspicions they were linked to the brand switch.
Pharmac has previously said it was critical that people who had been prescribed Logem did not stop taking it. If they had concerns, they should talk about their options with their doctor.
It said it would refund general practitioners for this visit, so the patient would not incur costs.
Pharmac said for most people, Logem worked in the same way as the other two lamotrigine brands - it had the same active ingredient and was delivered to the body in the same way and it would have the same effect as the other brands.
Logem had been approved for use in New Zealand by Medsafe, the New Zealand Medicines and Medical Devices Safety Authority, who are responsible for ensuring the quality, safety and efficacy of medicines.
Pharmac said approximately 80 million doses per annum of Logem are used in several countries, including Australia, Canada, Germany, UK, Spain, France, and the Netherlands.