The prime minister defended changes to the amount of prescription medicines patients can receive, following criticism from the opposition and pharmacists.

Under planned changes, up to six million people will be able to buy two months' worth of subsidised medicines with a single prescription, rather than just one month.

The doubling of prescriptions would apply to more than 300 medicines, including treatments for conditions such as heart disease, cholesterol, Crohn's disease

The Pharmacy Guild has warned the changes could lead to widespread medicine shortages, which would affect pharmacies in regional areas.

But Anthony Albanese said the measures would provide cost of living relief, while also promising to keep consulting with the guild on the proposal.

"What we won't do is ignore completely ... the cost of living pressures on people who have a health condition that requires regular drug treatment for the rest of their lives," he told parliament on Wednesday.

"(The opposition) can be angry, with all this fake outrage ... what we are doing as we are delivering .... cheaper pharmaceuticals."

Dozens of members of the Pharmacy Guild were in parliament on Wednesday to lobby MPs about the changes.

Guild president Trent Twomey said pharmacists supported measures to make medicine more affordable, there was a risk pharmacies would be impacted.

"Those cuts are going to mean that some pharmacies will have to reduce their hours ... what we're going to see is reduced healthcare services," he said.

"We are scared.

"We're scared because there's no detail."