Nearly 8,600 people received opioid-substitution treatment last year, which is normally used to treat an addiction to heroin.
It is an increase of 225 people on 2018.
According to details released under the Freedom of Information Act, 8,582 people received opioid-substitution prescriptions from a community pharmacist last year.
This treatment involves either methadone or the drug buprenorphine.
The figure for 2019 is up 3% on the year before and 6.5% on 2017.
Last year, 5,861 men and 2,721 women were treated.
By far the highest amount was in Dublin, at nearly 5,000.
After Dublin, the next highest county was Cork, with 581 people getting opioid-substitution treatment in their local chemist.
Limerick, Kildare, Wicklow, Louth and Galway also had large numbers.