The PSNI has seized several hundred ecstasy tablets from people attending a music event at the East Strand in Portrush in Co Antrim.
The drugs were recovered during a beach concert hosted by the DJ Fatboy Slim, which attracted 20,000 people.
Police arrested 11 people on suspicion of possessing drugs and of intending to supply them.
Officers also recovered quantities of herbal cannabis, cannabis and amphetamines.
Two people were also arrested at Upperlands, Co Derry on suspicion of possessing illegal drugs.
