Pharmacy peak bodies have warned changes to prescription prices in the upcoming federal budget will lead to more medicine shortages.

The government plans to allow people to buy two months' worth of subsidised medicines on a single prescription, rather than two separate prescriptions.

This means about six million Australians will pay less for their medicines, while also reducing the time they spend traipsing between their doctor's office and the pharmacy.

However, Pharmacy Guild of Australia president Trent Twomey said the changes could lead to further medicine shortages for patients.

"I'm all for cost-of-living relief and a cost-of-living measure, but this, unfortunately, is just smoke and mirrors," he told ABC TV on Wednesday.

"If you don't have the medicine in stock, how do you give double nothing? Double nothing is still nothing."

Mr Twomey said there were more than 470 medicines in the country that already had critical shortages or were completely unavailable.

The government said the changes, due to kick in on September 1, will deliver savings with patients needing fewer visits to the GP to get prescriptions.

Hundreds of common medicines will become cheaper to access under the policy, which is largely aimed at those with chronic conditions who spend a lot on medication.

People could save up to $180 a year, if their medicine can be prescribed for 60 days rather than 30, or more if their other medicines qualify for the extended dispensing change.

The more than 320 medicines on the list are for conditions such as heart disease, cholesterol, Crohn's disease and hypertension.

Mr Twomey said 40 per cent of the medications on the list were experiencing shortages.

"The government needs to stop worrying about a glossy announcement this morning about a pre-budget promise about how we're going to help with the cost of living," he said.

"It needs to get the basics right first, which is making sure that everyone can get at least one box."

Health Minister Mark Butler said the cost-of-living measure would address the issue of Australians delaying or going without medicines they need.

"Every year, nearly a million Australians are forced to delay or go without a medicine that their doctor has told them is necessary for their health," he said.

"This cheaper medicines policy is safe, good for Australians' hip pockets and most importantly good for their health."

Doctors will still be able to choose to write a prescription for a one-month supply for patients, rather than two.

Australian Medical Association vice-president Danielle McMullen welcomed the changes to prescriptions.

"At the time we're talking about so many cost-of-living pressures, this will really ease the burden on patients across Australia," she told Seven's Sunrise program.

"There are some situations of shortages in medicines at the moment but there will be a staged approach to this announcement to ease the burden on the shortages."

Meanwhile, just weeks out from the Albanese government's second budget, the opposition's Angus Taylor has called on Treasurer Jim Chalmers to lay down a path to bring the budget back to surplus.

The government should bank an expected commodity and income tax windfall and use it to lower the deficit, Mr Taylor said.

"If the government can't deliver a strong surplus with the current strong commodity prices and the strong economy left to it by the coalition, when will it ever deliver a surplus?"

Dr Chalmers has committed to absorbing most of the revenue bump from high commodity prices, but not to delivering a surplus.

© AAP 2023