More than a quarter of Irish teenagers started drinking at 13 or younger, new research has revealed.
A study of tens of thousands of 15 and 16-year-olds across Europe last year found as many as 7% of Ireland's young people admitted being drunk by the first year of their teens.
Boys were more likely to have drunk alcohol by that age.
The European School Survey Project on Alcohol and Drugs also recorded levels of drug use by teenagers, including 5% of 15 and 16-year-olds having used cannabis by the age of 13.
The study revealed 43% of the teenage group would have little problem sourcing the drug, while just over a fifth said the same about ecstasy.
On actual usage, 4% admitted using ecstasy, 3% cocaine, amphetamines, hallucinogens such as LSD or tranquillisers or sedatives.
In Ireland, 13% of teenagers had smoked cigarettes in the last 30 days - below the European average of 21%.
Three-quarters of Irish teenagers had had alcohol at some point by the time they reached 15 or 16 and just over a third said they had been drunk in the last month.
Drinking rates were higher among girls than boys.
The school survey project noted that the number of Irish teenagers who admitted smoking, drinking, gambling and taking drugs has fallen over the past 20 years.
The study also showed cannabis use was highest among teenagers in the Czech Republic, where drinking rates were also highest along with Greece and Hungary.
Ireland was among the countries with the highest rates of usage of new psychoactive drugs in 2015.
Some 16% of Irish teenagers also said they have gambled at least once in the last year, with just over one in 10 admitting their gambling was frequent.
Some 1,470 teenagers in Ireland were surveyed for the research project.
The European School Survey Project warned that the school/class participation rates in Ireland of 18% were exceptionally low.
It said that despite strict regulations on tobacco and alcohol, adolescents still report relatively easy access.
It also urged close monitoring of teenagers' use of the internet to identify patterns of addiction among children and adolescents.
Junior health minister Marcella Corcoran Kennedy said the figures on under age drinking are very worrying.
She said: "It is very worrying that the majority of these students started drinking before the age of 16 and that minors continue to have such easy access to alcohol.
"I am also deeply concerned that the pattern of binge drinking is still very widespread."
The minister said she was hopeful new legislation to restrict marketing and sale of alcohol, while also enforcing stricter health warnings, will provide further impetus for a continued decline in consumption.
Conor Cullen, of Alcohol Action Ireland, said it was important to remember the research was about children.
"We still have a long way to go in terms of protecting them from the large risks to their health and wellbeing from drinking alcohol at a young age, with over a quarter of them reporting having had their first drink at age 13 years old or younger," he said.
Mr Cullen said 15 and 16 is still too young for alcohol to be part of life.
"Children and young people are particularly vulnerable to alcohol-related harms and risks, as their bodies and brains are still developing - while the younger a child starts to drink alcohol the more likely it is they will develop problems with alcohol misuse in the future," he said.
"Therefore, delaying the age of drinking initiation is important for a child's health in both the short and long-term."