Patients must be put before profits, warns a peak body representing doctors as pressure mounts for the federal budget to address rising medical costs.

Treasurer Jim Chalmers is due to hand down the budget in four weeks as the cost of living increases along with the burden on the health care system.

The Pharmacy Guild of Australia has proposed the cap on medicine payments be reduced from $30 to $19.

But the Royal Australian College of General Practitioners wants a different approach, urging the government to extend the length of prescriptions and allow a larger supply of medicines to be prescribed in one go.

In a budget submission, the college argued allowing patients a two-month supply would halve dispensing fees which cost taxpayers $1.67 billion in 2021/22.

College president Nicole Higgins said this proposal would ensure consistency for patients who needed ongoing medication for illnesses such as hypertension and high cholesterol.

"This is a way of ensuring patients have access to their medication, it reduces their costs and improves access," she told AAP.

"It's about making sure people aren't running out of vital medications before the end of the month and going without."

Meanwhile, Pharmacy Guild president Professor Trent Twomey has written to federal MPs calling for their support on an 'Affordable Medicines Now' campaign to reduce the maximum co-payment of PBS medicines from $30 to $19.

Nine newspapers reported the letter to MPs warned doubling prescription lengths and increasing the amount of medicine available in each script could disrupt supply.

But Dr Higgins said the guild's proposal actually increased the cost to the taxpayer who would have to foot the bill for the $11 difference being pushed.

"The proposal from the guild is about protecting turf, not doing what is best for patients. It will cost people more and be less convenient," she said.

"This is part of a turf war between the guild and a small number of pharmacy owners and discount chemist chains. It should be about people and not profits.

"Let's rather think of solutions that are simpler, cheaper, easier and reduce the burden on the health system and the hip pocket."

Dr Higgins said any potential supply issues were about pharmacies managing their stock control.

"These are medications that are anticipated and planned for particular illnesses. There shouldn't be a difference in managing supply," she said.