Both brands of an ADHD treatment available in Aotearoa are in short supply due to a global increase in demand, Pharmac says.
In November, Pharmac switched 4000 patients to the Concerta brand of the drug methylphenidate, because the Teva brand faced supply issues.
An update on Pharmac's website said the country was now also running low on the Concerta brand.
"We switched people to Concerta brand to ensure everyone could continue to receive treatment.
"This has created supply concerns of some strengths of the Concerta brand of methylphenidate extended release," it said.
Pharmac had previously warned there would not be enough stock of Concerta for people to stay on the brand long-term.
It was now asking health professionals to switch people from Concerta back to Teva, when Teva is back in pharmacies.
"We have received clinical advice that it is safe to switch between the two brands."
Pharmac said it was expecting a large shipment of Concerta in February, but it may run low on 18 milligram strength stocks before then.