A number of products and equipment have been seized at what is believed to be an illegal steroid manufacturing site near Letterkenny in Donegal.
The Health Products Regulatory Authority (HPRA) says over 1,000 capsules of illegal products, believed to contain anabolic steroids, have been detained as part of the operation.
Unidentified powders, medicine labels and manufacturing equipment were also found.
This included measuring devices, glass vials for injections and a tablet press.
The operation was carried out on Thursday.
It involved HPRA enforcement officers working with An Garda Síochána and Revenue Customs officials.
The investigation is ongoing.
The HPRA is advising the general public to never purchase prescription medicines from unauthorised sources, as there is no guarantee as to their safety, quality or efficacy.