A quantity of ecstasy tablets as well as an amount of cannabis resin was recovered overnight in Co Monaghan.
Gardaí found the drugs, valued at over €2,000, in a car during a vehicle search on the N2 outside Castleblayney.
A man in his 20s, believed to be from Derry, has been detained by the Garda Drugs Unit in Monaghan.
He is expected to appear in court next week on charges under the Misuse of Drugs Act.
A number of other people were arrested but were later released. It is believed that they too may face charges.