Young people who mix energy drinks with alcohol are twice as likely to end up harmed than those who just drink alcohol, a study says.
Mixing energy drinks and alcohol is popular is nightclubs
Researchers from North Carolina's Wake Forest University quizzed over 4,000 US students about their drinking habits.
They found people who drank energy drink cocktails were more likely to suffer injuries, require medical help or get into trouble over sex.
The report said it was because energy drinks masked feelings of drunkeness.
Energy drinks typically contain high levels of caffeine as well as other stimulants such as ginseng. It has become popular among young people to mix them with alcohol, particularly vodka.
The web-based survey of 4,271 students, presented at an annual meeting of the American Public Health Association, found a quarter of those who had drunk alcohol in the previous 30 days had consumed energy drink cocktails.
Compared with students who did not mix alcohol with energy drinks, they were twice as likely to be hurt or injured, twice as likely to require medical attention, and twice as likely to travel with a drunk driver.
They were also more than twice as likely to take sexual advantage of someone else, and had almost double the risk of being taken advantage of sexually.
In a typical drinking session, they drank up to 36% more than the other students, and they also reported twice as many episodes of weekly drunkenness.
Lead researcher Dr Mary Claire O'Brien said: "We were surprised that the risk of serious and potentially deadly consequences is so much higher for those who mixed energy drinks with alcohol."
She said the problem was that students did not realise they were as drunk as they were when they mixed alcohol and energy drinks.
"Students whose motor skills, visual reaction times, and judgment impaired by alcohol may not perceive that they are intoxicated as readily when they're also ingesting a stimulant.
"Only the symptoms of drunkenness are reduced - but not the drunkenness. They can't tell if they're drunk, they can't tell if someone else is drunk.
"So they get hurt, or they hurt someone else."
And she added: "Students should be informed about the risks of mixing alcohol with energy drinks, as part of an overall programme to reduce high-risk drinking and its consequences."
Professor Martin Plant, an alcohol expert at the University of the West of England, said: "Energy drinks are a stimulant and any stimulant is associated with risk-taking behaviours.
"My advice would be that people should be aware of the risk and should not combine the two."