The two dance music fans who died after attending Saturday's gig in the Phoenix Park in Dublin had both taken a combination of drugs before suffering cardiac arrest.
Initial toxicology tests on the young men have now been completed.
They found that 22-year-old Shane Brophy, from The Swan, Co Laois, died after consuming cocaine and ecstasy.
He left the Swedish House Mafia concert before it ended and went to a party in a friend's house in west Dublin. He became ill there and died shortly afterwards.
The tests also established that Lee Scanlon (20), from Sorrel Heath, Clonsilla, in west Dublin, had taken ecstasy and cannabis.
He sought help at the medical tent at the concert after complaining of chest pains.
He was given CPR treatment to revive him but was pronounced dead shortly after he was admitted to James Connolly Memorial Hospital in Blanchardstown.
Drug-related deaths that involve cardiac arrest often include a mixture of substances.
The polydrug use can sometimes involve a combination of legal and illegal substances, according to experts.
Further toxicology tests are expected to be carried out following the completion of the post-mortem examinations.
But the initial tests have confirmed that neither of the young men had taken the so-called pink ecstasy, or PMA, which is regarded as a more lethal form of the drug.