The Irish Pharmacy Union has claimed that the health of some patients is being put at risk by a shortage of vital medicines.
Speaking at the IPU's annual conference, incoming President Rory O'Donnell said the latest example is the shortage of Eltroxin, a drug used to treat thyroid problems.
Mr O'Donnell says in many cases pharmacists typically receive little or no warning that these medicines are going out of stock, and there is often little information on when these stocks will be replenished.
He called on the Department of Health to ensure that an adequate supply of vital medicines is constantly available to minimise threats to patient safety.
In response, the Department of Health said medicine shortages can occur at times and accepted that there was a shortage of Eltroxin at the moment.
It said "considerable work is currently ongoing, involving all the relevant parties, and it is hoped that this action will alleviate the supply shortage in the very near future."
The department said it, along with the Irish Medicines Board, the manufacturers of drugs, wholesalers and the pharmacies themselves are all responsible for "securing a stable supply of medicines from a globalised market".
The IPU's annual conference is being held in Galway this weekend.