Palliative care doctors are warning of a difficult five months ahead as stocks of the most-used liquid morphine run out.
Around 1400 people every month use the 1mg/mL formulation, an essential pain drug.
But stocks are dwindling and expected to run out in December, due to the manufacturer - Pfizer - closing the factory in Australia.
Pfizer gave Pharmac two years' notice, but Pharmac said it had been unable to source an alternative.
It said it should have resupply of the formulation from April next year, but in the meantime doctors will have to give a double-strength dose, which patients will have to manage.
But end-of-life doctors said the situation was unacceptable and they were concerned for patient safety.
Dr Delamy Keall, senior medical officer of palliative medicine at Palmerston North Hospital and Arohanui Hospice told Nine to Noon patients got into a habit of taking a certain amount and when they were anxious, in pain or breathless may not remember that they need to take a different amount.
She said sometimes elderly were also living alone and managing their medications by themselves. Some may have poor eyesight, a tremor or cognitive impairment, which added further challenges when changing a habit they had learned.
"If they made a mistake and took their normal volume, but it's double the strength, then they're having double the dose. So that can cause drowsiness, confusion, sleepiness, may make them feel more unwell."
Keall said because the new alternative had not had time to go through full Pharmac approval, it would also become what was called a Section 29 - only be able to be prescribed by doctors.
"So for those patients who get their prescriptions from nurse practitioners, nurse prescribers or pharmacists prescribers, they will not be able to do that. They will have to find a doctor to prescribe for them over that period."
Chief executive of Hospice New Zealand Wayne Naylor said "given that there was two years notice and we knew that the manufacturing was going to stop and there was likely to be a period of non-manufacture in Australia, then I would have thought something could have been done".
He said one of the issues New Zealand faced was that drug companies were not interested in supplying the country because it was such a tiny part of the international drug market.
He said liquid morphine was cheap to manufacture.
"The raw ingredients are grown in Australia, so we should be able to have it easily manufactured for our region."
But he said drug companies were more interested in selling the high-cost opioid products
"So particularly in low- to middle-income countries, they have difficulties accessing this type of morphine because drug companies are selling and promoting the more expensive opioids - so fentanyl patches, things like that - rather than the very basics, which are just as good."
Palliative care specialist from Pharmac's Analgesic Advisory Committee Dr Catherine D'Souza said Pharmac's competitive bid process did not receive any traction with drug companies, so they had to find an alternative.
She said the factory would be taken over by the Bridgewest group next year and supply would resume.
"You could argue that Pfizer has a responsibility to keep producing these essential medicines until such time that the new company were able to take over," D'Souza said. "I don't know what happened between the companies, but something happened to lead to this delay.
"I would be utterly ashamed of Pfizer if it is indeed because they're not making enough profit and therefore they were to leave us all in this difficult situation."
She said going forward, looking at diversifying supply was something that the Analgesia Committee would be strongly advocating for.
"We shouldn't be in this situation."
A Pfizer spokesperson said in a statement: "As a result of the evaluation of our global manufacturing network, Pfizer decided to discontinue the manufacturing of RA-Morph and its supply in New Zealand. The Perth site was divested in April 2023 and purchased by Bridgewest Group - the sale having closed on 4 April 2023.
"The transfer of sponsorship of RA-Morph was Friday 22 September and supply was available from Bridgewest on Monday 9 October. Pfizer and Bridgewest worked cooperatively to ensure continuity of supply to customers in New Zealand was maintained in the interim.
"Pfizer has been in regular communication with Pharmac on medicines supplied from the Perth site. In the interest of patients, and to ensure that the market had lead-time to seek alternative means of supply, a discontinuation notice was given to Pharmac with two years' notice in September 2021."