Around €1m worth of drugs were seized last night as part of a planned Garda Operation in Longford town and South Roscommon.
Four people have been arrested in connection with the seizure of what is believed to be almost 2,000 cannabis plants.
Around 800 cannabis plants were seized at a growhouse in the South Roscommon area where a man in his 20s was arrested and is presently being questioned at Roscommon Garda Station.
It is believed double the number of plants has been seized at a growhouse based at a commercial premises in Longford town.
Three people in their 20s and 30s were arrested at the scene and are being held at Longford and Mullingar Garda Stations.
All four are being questioned under section 2 of the Drug Trafficking act and can be held for up to 48 hours.
The operation was part of a co-ordinated planned search by the Roscommon Longford Drugs unit, the technical unit in Roscommon, uniformed gardaí in the division backed up by the Garda national drugs unit.