A man was being quizzed after the seizure of 3.5 million euro of drugs.
Some 400kg of cannabis resin and 50kg of cannabis herb were discovered during the intelligence-led, planned raid on a premises near Malahide Road, Coolock, north Dublin.
About 8kg of tablets - which are yet to be analysed - were also found.
The joint operation was carried out between the Garda National Drugs Unit and Revenue Customs.
A suspect aged in his 20s has been detained at Santry garda station under the provisions of Section 2 of the Criminal Justice (Drug Trafficking) Act 1996.