Officers say they were detained following searches at properties in the Pallasgreen area this morning.
All 4 are in their 20's and are being held at Henry Street, Mayorstone and Bruff Garda stations, under Section 50 of the Criminal Justice Act.
They can be held for up to 7 days without charge.
Members of the Garda Regional Support Unit and the Limerick City District Detective Unit joined colleagues from the Bruff District for the operation.
