A country-wide shortage of morphine is impacting those in palliative care, while more stock could be months away.

The daughter of woman who is dying from stage four lung cancer says her mother is in considerable pain and she is "appalled" by the drug shortage.

Crown entity Pharmac confirmed it is expecting gaps in the supply of morphine oral liquid this month.

"Unfortunately, there will be times in April when morphine oral liquid will be unavailable," Pharmac said on its website.

"We are encouraging clinicians to consider treatment alternatives now to preserve morphine oral liquid for people who need it the most."

The availability of morphine oral liquid varies by location, Pharmac said.

Jennie McKeown said her mother has stage four lung cancer and hasn't been able to get morphine to help with her pain.

"I first heard in late February from my mother's hospice nurse explaining why my mother couldn't be prescribed morphine.

"I was incredulous."

Four weeks later both McKeown's mum's pharmacist and GP confirmed there was none available still.

"I was absolutely appalled," McKeown said.

"She hasn't got very long to go, and she is in a lot of pain."

Her mother has been given OxyNorm, a semi-synthetic opioid capsule, which she was taking well, but McKeown was concerned for those who need morphine.

"OxyNorm was offered in its place as a similar opioid but I understand some people get nausea with it and can't tolerate Oxynorm."

Concerns about the shortage of low-dose morphine had health workers worried in November last year. The stocks were 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 at the time.

Pfizer's factory and morphine production was taken over by another company, Bridgewest, but it was unable to supply New Zealand until June.

Pharmac said it has secured two brands, Wockhardt and Oramorph. Supply of Wockhardt is low and Pharmac has been advised of potential delays to the delivery of Oramorph.

"Pharmac has been looking for alternative brands of morphine oral liquid for at least 18 months," Pharmac's website said.

"Unfortunately, finding both short and long-term supply has been challenging.

"The logistics of making and supplying controlled drugs, like morphine oral liquid, is [sic] complex."

Pharmac said it is working closely with suppliers on permits and labelling to speed up the delivery of stock to New Zealand.

Morphine wasn't the only drug New Zealand has experienced shortages of recently.

Up to 4000 New Zealanders with ADHD were forced to switch medication after supply problems with methylphenidate, and recently the supply of Concerta has been an issue.

There are also global constraints on some diabetes treatments.

The suppliers of both dulaglutide and liraglutide have advised Pharmac that they can only secure enough stock for current patients.

New prescriptions are now restricted to people with type 2 diabetes who are high-risk and have no other appropriate treatment options.

-This story was first published by the New Zealand Herald.