Pharmacists have been told to restrict the number of paracetamol tablets they give out because of a national shortage of the country's most dispensed medicine.

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About a million paracetamol tablets are dispensed every day, requiring two shipping containers to be imported every month.

Stocks are running low and new supplies aren't expected until the New Year.

A month ago the drug-buying agency Pharmac wrote to the country's pharmacists instructing them to place restrictions on the way the drug was dispensed.

Pharmac's director of operations Lisa Williams said the shortage was due to issues at overseas manufacturing plants.

"One of the manufacturers of the active pharmaceutical ingredient in the world, had a fire which caused a problem at their factory with the production of the product," she said.

"That means all finished product manufacturers of paracetamol have been finding difficulties getting access to the active ingredient."

Those restrictions mean patients who experienced acute pain, can receive up to a 100 tablets at a time - about 12 days' worth.

And those with chronic illness can get up to 240 tablets, about a month's supply.

The restriction applies only to paracetamol bought on prescription - it is still possible to buy the drug off the shelf at a chemist or supermarket.

Pharmacists like Melina Holmes, who owns a Unichem Pharmacy in Whanganui, said since the restrictions came into place she had seen the amount of paracetamol the pharmacist dispensed drop by about two thirds.

But she said such restrictions impacted both pharmacists and the public, including extra time talking to customers and calling doctors.

"Which means we have to do extra dispensings of those medicines, which is extra time that it costs us in staffing, labelling, your vials and boxes," she said.

"It also means it's an inconvenience to the customer, they have to come back on some medicines on a monthly basis, when they used to just come every three months for that particular medicine."

"No one reimburses the pharmacy or the customer for that inconvenience" she said.

She said the issue with paracetamol tablets came after restrictions on paracetamol liquid and ibuprofen ibuprofen tablets had just been lifted.

Ms Holmes, who has been a pharmacist for 20 years, said it was part of a worrying trend, with the number of restrictions seemingly on the rise.

"Even five years ago if we had a shortage on a medicine it was very rare," she said.

"Whereas now if you look at the last six months it's becoming a little bit of a joke in terms of pharmacy, that you go, 'what's out of stock this week?'.

"We have a whiteboard in our pharmacy and we write out all the out of stocks."

But Pharmac's Lisa Williams said while they were finding it more difficult to access drugs - part of a worldwide trend - it was rare for shortages to impact on pharmacists or the public.

She said because Pharmac tended to contract drugs through a single supplier, the country experiences fewer stock outages at a patient level than other countries.

Pharmac has also begun funding an alternative, although it too is in limited supply.

Ms Williams thought it was unlikely the country would run out.

"There's lots of other pain-management medicines that could be used, that would be what doctors would need to consider prescribing."

If those medicines were more expensive, Pharmac would reimburse pharmacists and then seek compensation from the supplier of paracetamol.

"But I think that's a very unlikely scenario," she said.