The cost of buying hundreds of medicines from pharmacies will be up to 40% cheaper from today.
The Irish Pharmaceutical Healthcare Association says nearly 300 familiar medicine brands are included in the price cuts.
The move is aimed at reducing costs to the State by €94m over the next year.
The Irish Pharmacy Union, which represents pharmacists, says the move is good news for patients, particularly those who do not qualify for a medical card.
However, it says pharmacists who bought medicines for patients on behalf of the Health Service Executive before today had to pay the old price, and could lose out, as they will only be reimbursed by the HSE at the new lower price.
Patients can find out if the price of their medicine has been cut on a special website, checkthelist.ie, or by ringing lo-call 1890-876700.