They charged a 22-year-old man from Bankstown with supplying a greater than commercial quantity of drugs after he was allegedly found with 20 packets of GHB.
Speaking to reporters on Sunday, NSW Premier Gladys Berejiklian vowed to do everything in her power to shut down the event and stop it from returning to the state following the "absolutely tragic" deaths.
'I never want to see this event held in Sydney or NSW ever again.
"Installing police with drug dogs at festivals only causes people to panic-swallow all their drugs at once, so it's no wonder that people overdose", it posted.
A 19-year-old man from Artarmon was flown from the festival to Westmead Hospital in a critical condition.
Australian Medical Association president Tony Bartone says law enforcement can't be the sole strategy when it comes to dealing with illicit drugs.
A 26-year-old man from Albury died at the same event in 2015, as did a 23-year-old two years before that.
"I'm absolutely aghast at what has occurred, I don't want any family to go through the tragedy that some families are waking up to this morning, it's just awful to think about", the premier of the Australian state of New South Wales, Gladys Berejiklian, said.
"How many funerals do we have to go to of people that have taken these substances and found out they're not what they're sold?" asked Liberal backbencher Warren Entsch during an interview with ABC Radio in May.
A further two men and three women were also charged with supply drug offences.
Police have been told an additional 13 people attended Nepean Hospital for treatment for drug-related issues, while as many as 700 people sought assistance from medical staff on-site.
The Defqon 1 festival, held at the Sydney International Regatta Centre, plays mostly hardcore techno, house and trance music. Among them were two girls, both 17, said to have been carrying 120 MDMA capsules.
"This means that all types of soft and hard drugs are prohibited".
Defqon.1 organisers had previously warned ticket holders that the festival had a zero-tolerance policy.
The organisers of the festival have come out and said: "We are disappointed at the number of reported drug-related incidents, we have a zero-tolerance policy in relation to drug use at the festival". It has since offered its "thoughts and prayers" to the suspected drug victims.
Local detectives have formed a new police strikeforce, dubbed Highworth, to investigate the two deaths. Festival organisers are working closely and cooperating with the authorities regarding the fatalities and the number of medical presentations made during the evening, a full investigation is now underway.
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