Police have revealed the concertgoers who were hospitalised in a critical condition during the Listen In event in Auckland on Friday had consumed MDMA.
Four people were also arrested for disorderly behaviour offences during the event at Mt Smart Stadium for climbing on top of the huge 25 metre high marquee.
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In total five people who attended the Listen In on October 4 were hospitalised, with three patients rushed to Auckland Hospital in a critical condition after taking drugs.
One person who had taken drugs was in a moderate condition, and a fifth person's injuries were unrelated to drugs.
"Police were made aware that several people attending the event required hospital treatment after consuming what the users believed to be the illicit substance MDMA," Auckland City operations manager Inspector Siaosi Fanamanu told the Herald.
"We have spoken to some of these people who have admitted they did not know what was in the substance they were taking.
"In this instance we have provided prevention advice to these people about the use of illicit drugs."
MDMA is a psychoactive drug, otherwise known as ecstasy, resulting in increased energy, empathy, and pleasure.
The Listen In concert drew 20,000 people to what was sold as "the largest marquee in Australasia" erected on Mt Smart's field, to watch high-profile international acts Flume, Diplo and ScHoolboy Q.
Police said they were not overly concerned with the conduct of the attendees in general.
"This was a large event and overall police were pleased with the behaviour of those attending," Inspector Fanamanu said.
In the coming weeks, police said they will be meeting with the organisers of the Listen In festival, run through Auckland Stadiums which oversee Mt Smart.
"As is our standard practice with events of this nature, we will undertake a debrief with the organisers of the Listen In festival and other involved parties," Inspector Fanamanu said.
"This will assist in the identification of areas of concern or any risk behaviours and enable measures to be put in place so organisers can improve the experience for concert-goers at future events."
However, many concert-goers described the wild scenes on Friday as like nothing they had ever witnessed.
"It was actually quite insane. Towards the end of the night you could really see the impact of whatever they had taken," one woman said.
"I remember looking down and there was literally a girl being wheeled out of the concert unconscious. Her head was like back, her mouth was open, body was limp.
"Then I saw a chick being walked out of the mush pit and she was fully chewing her lips. She was on something. She was chewing her lips like bloody nobody's business."
She stayed at the venue after the concert had finished to look for some jewellery.
"There were so many of the little bags that you put drugs in, they were littered all over the ground. They were everywhere."
"You could definitely see there was quite a big drug presence there."
Auckland Stadiums director James Parkinson, who oversees Mt Smart Stadium, said security checked bags of concert-goers and patted down "profiled individuals".
"We had safe disposal units for drugs at all gates and a volume of drugs were confiscated from patrons at the gates. Both security staff and police were monitoring the site for drug use throughout the event."
Parkinson said they considered inviting Know Your Stuff NZ - who test drugs at festivals - to the event.
"However, these drugs are illegal substances and are prohibited items in our venues. The concept of testing and returning illegal substances to patrons places us, as a venue operator, in a very difficult legal position," Parkinson said.
Parkinson denied there was widespread drug-taking.
"We had very good security measures in place, which meant the vast majority of the over 20,000 crowd had a great night.
"Unfortunately, these incidents do highlight the inherent risks of drug-taking."
Auckland Hospital confirmed today only one patient who had been admitted on Friday night was still in hospital.
Dr Jez Weston, from Know Your Stuff NZ said: "this year we've been seeing people take too much MDMA, cathinones and people taking unknown and new substances.
"Fundamentally, young people shouldn't have to suffer from a night out and that's what we're trying to achieve here."
Footage of numerous concert-goers climbing on top of the tent, which had been flown from Australia, also emerged.
Within the tent itself, audience members could be seen climbing the metal support pillars, many metres above the crowd.