The powerful pharmacists lobby warns pensioners they won't see any benefit if they buy discounted medicines.
The Pharmacy Guild fired the warning shot on Monday, after Chemist Warehouse announced it would discount prescription medicines by $1 from January 1.
Pharmacists have been required to charge set fees for prescription drugs - $6.10 for concession patients and $37.70 for general patients, although this will rise to $6.20 and $38.30 next year.
But in 2016 they'll have the option of providing a $1 discount, under the federal government's new $19 billion five-year agreement with pharmacists to dispense medicines listed on the pharmaceutical benefits scheme.
The guild is opposed to the optional discount, arguing it will delay access to free medicines for the sickest and most medicated people because they will take longer to reach the $366 safety net threshold.
Concessional patients would need to fill an extra 11 prescriptions a year to reach the safety net, Guild spokesman Greg Turnbull says.
Consumers could be misled into believing they will benefit "when they are actually no better off over a 12-month period".
The government's decision to take some over-the-counter medicines such as painkillers off the PBS will also delay access to the safety net for some patients, Mr Turnbull said.
Health Minister Sussan Ley says the optional discount will increase competition but has admitted some patients, especially in rural areas, will miss out because not all pharmacists will offer it.
The optional $1 discount, which would come out of pharmacist coffers, would potentially save taxpayers $360 million over five years.
