Alcohol was strongly associated with underage sex
Young adults in Europe deliberately binge on drink and drugs to improve their sex lives, research suggests.
The UK has one of the worst reputations for binge drinking and underage sex but there are striking similarities between countries, a study found.
A third of 16 to 35-year-old men and 23% of women questioned said they drank to increase their chance of sex.
The study - of 1,341 young people in nine countries including the UK - is published in BMC Public Health.
Young people were also more at risk of unsafe sex while under the influence of alcohol or drugs, the study found.
The researchers said although it was well known that use of alcohol and drugs was linked to risky sexual behaviour, this study showed many young people were "strategically" binge drinking or abusing drugs to improve their sex lives.
They questioned young people in nine cities, one each in the UK, Germany, Austria, Czech Republic, Greece, Italy, Portugal, Spain and Slovenia - who all routinely went to pubs, bars and nightclubs.
Early use of alcohol and other drugs was closely linked to having sex under the age of 16 years, in all countries, especially in girls.
Almost half of participants in Vienna, Austria had drunk alcohol and had sex by the time they were 16 compared with 36% in Venice, Italy, 37% in Palma, Spain and 30% in Liverpool.
The same was true for those who took drugs under the age of 16 but there were variations in popularity of different drugs among different countries.
More than a quarter of youngsters taking cocaine said they used it to prolong sex and drug use in general was linked to having multiple partners.
Drunkenness and drug use were found to be strongly associated with an increase in risk taking behaviour and feeling regretful about having sex .
Those who had been drunk in the past four weeks were more likely to have had five or more partners, sex without a condom and to have regretted sex after drink or drugs in the past 12 months.
Cannabis, cocaine or ecstasy use was linked to similar consequences.
Study leader Professor Mark Bellis, director of the Centre for Public Health at Liverpool John Moore's University said: "Millions of young Europeans now take drugs and drink in ways which alter their sexual decisions and increase their chances of unsafe sex or sex that is later regretted.
"Yet despite the negative consequences, we found many are deliberately taking these substances to achieve quite specific sexual effects."
He added that strategies to reduce substance abuse and encourage safe sexual behaviour needed to take into account the fact that the two were inextricably linked.
Simon Blake, chief executive of Brook, said: "When it comes to drugs and alcohol young people learn from us, the adults who help determine the culture in which young people are learning about sex, and learning about drugs and alcohol. "Sex and relationships education also needs to include more discussion about the association between alcohol, drugs and unsafe sex."
Frank Sodeen from Alcohol Concern said: "The report is a good reminder of the multiple dimensions of drink-related harm."
He added local authorities need to think as broadly as possible about projects to reduce alcohol use and incorporate issues such as sexual health.