Drugs worth £500,000 have been seized by the police in Ballymena.
The pills known as BZPs replicate the effects of drugs like ecstasy, police said.
100,000 of them were found in a storage facility near the Showgrounds in the town on Tuesday. There were no arrests.
An Organised Crime Branch spokesman said the drugs, although legal, are "potentially lethal particularly where young people are concerned".
"We are delighted to have taken these out of circulation," the spokesman added.
As a result of the seizure, police are liaising with the Department of Health Medicines Inspection and Investigation Branch.
Police said two people had died in the last year in England as the result of taking BZPs.
Last week, the Home Office said the drug would be banned by the end of the year.
September 2, 2009