HUNTINGTON, W.Va. (AP) — Officials in Huntington are warning people about an especially dangerous batch of heroin after emergency responders responded to more than two dozen reported overdoses within a four-hour span.

Cabell County EMS Director Gordon Merry told news outlets that all the victims had been revived Monday using naloxone. Merry said the heroin that the users had taken was laced with a substance so strong that it sometimes took more than one dose of the opioid overdose-reversing drug to revive them.

Most of the 26 reported overdoses reported Monday were in an area surrounding Marcum Terrace, leading officials to believe the cases were connected.

Cabell County responded to 39 overdose calls in all of August 2015.

As of late Monday, officials were not sure what substance the drug had been laced with.