Psychoactive drug use among young Irish people is the highest in Europe
The HSE is warning that the strength of ecstasy pills and MDMA has increased massively.
The health service issued the warning as Ireland's festival season gets into full swing.
It comes in the wake of a number of incidents at the Life festival last week.
Separately two young people died after taking drugs at a festival in England last Saturday.
Dr Eamonn Keenan says the safest option is to not take drugs at all.
"It is the strength of the MDMA that is giving us a little bit of concern at the minute," he said.
"It is about getting the message out to the festival goers so they enjoy the festival and don't have the adverse effects.
"We had a festival last week in Life where there were a number of people who ended up in hospital after taking drugs."
Psychoactive drug use among the 15 - 24 age group is higher in Ireland than anywhere else in Europe according to the HSE.
The executive said the strength of most illegal drugs is on the rise with a more varied and accessible market.
Some of the adverse affects reported recently include seizures, overheating and mental health problems - in particular paranoia and psychosis.
Tony Duffin CEO of Ana Liffey Drug Project said it is safer not to use drugs at all "but we know that over the summer some festival goers will choose to use such drugs."
"We want everyone who goes to a festival this summer to come home safely.
"If you do choose to use drugs – inform yourself first. Harm reduction works, it could save your life or the life of a friend.”
While warning that it is "always safer not to use ecstasy" the HSE has published this checklist for those that do: