Emma McDonnell, of the Graduate Entry Medical School, University of Limerick, said there was a 208pc rise in the prescribing of codeine between 2006 and 2016.
It is also available in some over-the-counter products and it is difficult to monitor if a particular patient is "codeine shopping" - travelling to different pharmacies to buy it.
"Without medical supervision, a large proportion of the Irish population is self-medicating with codeine and many have unknowingly developed an addiction," she said.
"Those who suffer from a codeine addiction often tell how their relationship with the drug started so innocently in the quest for pain relief and they had little to no understanding of the truly addictive nature of the drug."
Source: Eilish O'Regan, Irish Independent, 16th April 2019