For teenagers, mixing energy drinks with alcohol is like taking cocaine, according to a new study.

United States scientist Richard Van Rijn, an assistant professor in medicinal chemistry and molecular pharmacology at Purdue University, says the harmful cocktail appears to trigger changes in the adolescent brain similar to taking the illicit drug, and that the effects last into adulthood.

Energy drinks, often marketed to teens, can contain between 6mg and 240mg of caffeine per serve. For many this is about 10 times the caffeine in soda - a common beverage mixed with alcohol.

But little is known about the health effects of the drinks when consumed with alcohol.

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A new study, published in journal PLOS ONE, found adolescent mice given caffeinated alcohol became increasingly more active, much like mice given cocaine. Neurochemical changes in the brain were noted.

Levels of the protein FosB, which is a marker for long-term changes in neurochemistry, were elevated in levels similar to those abusing drugs such as cocaine and morphine.

"It seems the two substances together push them over a limit that causes changes in their behaviour and changes the neurochemistry in their brains," said van Rijn.

"We're clearly seeing effects of the combined drinks that we would not see if drinking one or the other."

Worryingly, when the same mice had grown to adult age, they had become "somewhat numb" to the rewarding effects of cocaine.

"They may then use more cocaine to get the same effect."

- AAP