Gardaí in Co Laois seized drugs "within minutes" of the gates opening at this year's Electric Picnic festival.
The doors opened at the Stradbally event at 4pm yesterday with around 57,000 people expected to attend over the three days.
A number of drug seizures were made by gardaí yesterday, with people found in possession of cocaine, ketamine, LSD and MDMA when attempting to enter the gates.
Gardaí wished to remind people attending the festival that any seizures made "will have consequences for the individual" and that "keeping people safe and free from harm is important".
It is not known whether any arrests were made following the seizures or whether subsequent discoveries have been made since the initial report by gardaí yesterday.
A garda spokesperson said they would be unable to provide this information until the festival is over.
Earlier this week, the HSE issued an advisory for people attending festivals to "play it safe" when it comes to drug-taking.
The health service said that while it does not condone drug use, it said "we need to be realistic" in acknowledging that people may try drugs for the first time or new types of substances when attending festivals.
“The HSE is aware that across Europe in the last couple of years there has been a significant increase in the strength of MDMA/Ecstasy, which means increased risks for users," said Dr Eamon Keenan, the HSE’s National Clinical Lead-Addiction Services
"This is likely to be reflected in Ireland also. If you do decide to take drugs, you should be aware of this issue and you can access our harm-reduction advice around festivals at www.Drugs.ie/festivals.
"One of our key messages here is ‘Start low, go slow’, reflecting this likely increase in the strength of MDMA/Ecstasy. If you feel unwell after taking any substance, go immediately to the Medical Tent and be honest with the medical staff about what you have taken. They are not there to judge, only to help," he said.
The HSE advises people who will be taking drugs to start slow with a small dosage, don't mix different types, stay hydrated and to seek help if someone becomes unwell.
The message came ahead of International Overdose Awareness Day tomorrow which aims to create a better understanding of overdoses and reduce the stigma associated with drug-related deaths.
"This year International Overdose Awareness Day coincides with the first day of one of Ireland’s biggest festivals. Our message is clear; overdose does not discriminate," said Dr Keenan.
He cited the HRB National Drug-Related Deaths Index* which shows that 736 people died of overdoses in 2016 compared to 431 in 2004, an increase of 71%.
"Many of these deaths were premature – half of all deaths in 2016 were aged 42 years or younger. Alcohol, mixing drugs and prescription drugs were the biggest contributors to overdose deaths," he said.
The HSE would continue its rollout of naloxone, a medication used to counteract an overdose caused by opioids, and will be establishing a working group in response to the increased strength of MDMA and ecstasy across Europe.
An event to remember those who have died from an overdose will be held today by the HSE, the Department of Health, the Students Union of Ireland and partner agencies with the theme being ‘Time to remember, time to act. Every life is worth saving’.
Among the speakers will be Minister of State at the Department of Health Catherine Byrne; Dr Phillip Dodd, Clinical Advisor to the HSE National Office for Suicide Prevention; Dr Eamon Keenan; Dr Denis O'Driscoll, The Naloxone Project; and Roisin O'Donovan, Vice President for Welfare at the Union of Students in Ireland.
The Ana Liffey Drug Project is again providing welfare and outreach teams at this year's Electric Picnic with harm reduction advice.