The Government is losing millions of euro each year by not swapping branded medicines for generic versions.
Medicines for Ireland says €25 million could have been saved last year by changing just one arthritis drug to a similar unbranded version.
When the patent for a high-priced branded medicine expires, pharma companies are able to create cheaper copies.
Chief Pharmacist with University Hospital Galway John Given said the State is too slow to make the swap.
"The Uk switch over happens within a year. For one of our biosimilars, it took over six years to get to maximum savings.
A biosimilar is after patent runs out in a biological drug, companies are allowed make copies of it, so basically it's just a copy of a drug that's already run out of its patent.