The Health Service Executive has warned that "high strength" drugs have been identified at Electric Picnic, now underway in Stradbally, Co Laois.
The HSE has an anonymous drug testing facility at the festival for the first time.
It is part of its ongoing drug harm reduction campaign.
Electric Picnic concert-goers can choose to anonymously submit substances in a 'surrender bin' at the HSE testing tent.
Experts can then identify and communicate if extra dangerous substances are in circulation - and the HSE has now issued its first alert.
In a tweet it warned: "We are issuing a caution from Electric Picnic 2022.
"The HSE lab has identified a Mybrand purple skull pill as high strength MDMA - it is approximately two times the average adult dose.
"Please exercise caution and remember it is safer not to use drugs at all."
The @drugsdotie team are issuing caution from #EP2022.— HSE Ireland (@HSELive) September 2, 2022
The lab on-site has identified Mybrand purple skull pill which is approximately two times the average dose.
Please exercise caution. Visit https://t.co/Z58KqtOZpU.#ReduceTheHarm pic.twitter.com/zvYuix8hnm
Professor Eamon Keenan, HSE National Clinical Lead, Addiction Services said at the launch of the new drug testing tent last month, that he believes the measure will have an impact and "save lives".
He said: "We are currently very concerned about the emergence of new psychoactive substances and high potency substances which pose a threat to health.
"This project will provide us with vital information that we otherwise can't access in real time.
"While this is a progression, the HSE messaging will remain clear, it is safer not to use drugs at all.
"For those who choose to, they should still follow the practical steps recommended by the HSE to reduce the harms."