The HSE is warning that the younger people start to drink, the more likely they are to take drugs.
Parents are being urged to talk to their children about alcohol ahead of the Junior Cert celebrations tomorrow.
The health service said key cognitive development takes place between the ages of 12 and mid-20s, and alcohol has a negative impact on the brain's function.
Dr Bobby Smyth, a Consultant Child and Adolescent Psychiatrist, said planning a supervised event is the best option.
Dr Smyth said: "The kids who are drinking heavily at a younger age are the ones most likely to start adding in other substances into the mix and there are growing concerns and appropriate concerns.
"We are seeing it in the health sector around cocaine use and MDMA use, and it's the kids who drink the most who are most likely then to add those things to the cocktail."