A teenager posted an image showing a variety of drugs and alcohol ahead of a gig at Belfast's Odyssey arena in which dozens of casualties were treated outside for the ill-effects of substances.
The teen shared a photograph - showing pills, powder, vodka and cider - on Facebook - several hours before a gig by Dutch DJ Hardwell at the arena.
He posted the message: 'Well ... Hardwell'
This afternoon, police confirmed that an 18-year-old man had been arrested on suspicion of being possession of class A controlled drugs with intent to supply.
The post came several hours before dozens of young people were treated for the effects of drugs and alcohol outside the venue.
The ambulance service declared it a 'major incident', with up to 60 casualties.
The Belfast Trust confirmed 14 young people are now at the Royal and Mater hospitals in a stable condition.
Extra staff were brought in to nearby Belfast hospitals to deal with the high numbers of casualties.
According to the Odyssey's general manager, Adrian Doyle, those who arrived at the gig intoxicated were not allowed in.
"It is our understanding that a number of patrons arriving at the Odyssey Arena to attend a concert by Dutch DJ act ‘Hardwell’ have required medical attention, having arrived intoxicated at the Odyssey Complex," he said.
"These patrons were not granted entry to the Odyssey Arena, and were treated by the Ambulance Service outside. Seven patients have now been transferred to hospital by ambulance."