Over 700,000 units of illegal medicines were seized in the first six months of the year, according to the Health Products Regulatory Authority (HPRA).
The HPRA said it represents a sharp increase in the volume of illegal medicines compared to the same period last year, when over 551,580 units were seized.
The most significant categories of illegal products detained included anabolic steroids (23%), analgesics (14%), sedatives (11%), and erectile dysfunction medicines (10%).
The authority has emphasised the serious health risks posed by prescription medicines being bought online from unauthorised sources.
It said there is no guarantee about the safety or quality of illegal prescription medicines purchased outside of the regulated pharmacy setting.
Grainne Power, HPRA Director of Compliance, said there was a notable rise evident in detentions of Semaglutide, a drug used for diabetes or weight management.
These drugs also go under the brand names of Ozempic, Rybelsus and Wegovy.
Ms Power said that while the overall numbers of Semaglutide detained are small in comparison to other products, the first six months of this year saw almost triple the volume of illegal units of Semaglutide detained, compared to all of last year.
There were 783 units of Semaglutide seized in the first six months of this year, compared to 286 for all of last year.
The HPRA said that as part of enforcement measures, 1,603 e-commerce listings and or social media pages were amended or shutdown.
The HPRA works in co-operation with An Garda Síochána and Revenue's Customs Service.
