Nearly 5,000 young people who had been followed since the age of nine as part of the Growing Up in Ireland study were asked about their use of eight substances, including alcohol, e-cigarettes, tobacco, cannabis, cocaine, ecstasy, ketamine and other drugs.

The study found half of Irish 20-year-olds are drinking at risky levels, while almost a tenth are classed as high-risk drinkers, and 5% show signs of possible alcohol dependence.

The study also found 38% smoked tobacco, almost a quarter used cannabis, 23% had used cocaine in the previous year, 18% ecstasy, and 12% had taken ketamine.

Dr Deirdre Mongan, one of the authors, expressed particular concern about the risks of mixing of cocaine and alcohol.

“Cocaine would be a feature of both the polydrug use and the heavy polydrug use. Cocaine has become such a problem in Ireland, and its use has become widespread among this group," she said.

“We do know from other surveys that those who use cocaine, the last time they used it, 95% used alcohol at the same time, and that's something that's very concerning. 

When you take cocaine and alcohol together, it’s actually much worse than taking either on its own.

“It creates a new substance called cocaethylene, which has a longer half-life than cocaine, leading to a much higher risk of heart attack, stroke, and sudden death than using either substance alone."

She said some people use cocaine to extend the effects of alcohol, "which is worrying, because of the risk of experiencing health harms are greater when they are used together".

“We also see people who use ketamine, the last time they used it quite a high proportion used MDMA, a high proportion also use cocaine and alcohol.”

She noted drugs had become more affordable and had increased potency.

“The MDMA in circulation now is much stronger than what it used to be. The cocaine in Ireland now compared to 20 years ago is a lot purer and stronger, and again, that's increasing the risk of overdose and harms from the drug.” 

Dr Mongan said the trend of polydrug use emerged with the arrival of new psychoactive substances around 2010.

“These are synthetic drugs, that mimic the effects of drugs, such as cannabis, cocaine, MDMA. Since then, we've seen that proliferation of new drugs on the market. There would not have been the same range of drugs available in Ireland before 2010.

“This type of poly drug use is quite new. We don’t really know what the impact of using all these substances together is because we’re only beginning to gather the data now.”