Fourteen young people were treated in hospital overnight after dozens of concert-goers fell ill in Belfast.
Heavy drinking revellers were planning to attend a rave in the Odyssey Arena on the edge of the city centre.
Charity volunteers gave first aid outside the venue and paramedics and doctors arrived. Up to 50 people are thought to have become unwell.
The patients are all in a stable condition, a hospital spokeswoman said.
Dutch electronic dance DJ Hardwell was performing inside the venue.
A spokesman for the Northern Ireland Ambulance Service said: "We believe the majority arrived suffering from too much alcohol."
He added a number of people were unconscious at the scene.
Hardwell was named the world's number one DJ in the 2013 DJ Mag Top 100 DJs Poll.
His hits include Spaceman, Three Triangles (Losing My Religion) and Apollo.
Last month dozens of fans camped overnight or queued for hours on a Belfast street in pouring rain for a ticket to his show.
Colin Neill, chief executive of Pubs of Ulster which represents local bar owners, said: "Pubs of Ulster would reiterate that alcohol should be consumed responsibly and safely.
"Pre-loading at home before going out is dangerous and can lead to unintended consequences with people putting themselves at great risk."
Odyssey general manager Adrian Doyle said, as with any concert, the safety of patrons was an absolute priority at all times and the event control team was confident that it had sufficient staff on site to maintain a safe and enjoyable concert.
The young people, thought to be teenagers, were treated at the Royal Victoria and Mater hospitals in Belfast.
A helpline for concerned parents has been established at 02890638131.Suggest a correction