[Lead scientist Maria Lucia] Souza-Formigoni and her colleagues found that volunteers in both groups felt they had better motor coordination when drinking alcohol mixed with the energy drink than when they consumed alcohol alone.

But in a test of motor skills where subjects had to transfer pegs on a board, those drinking alcohol mixed with an energy drink did not perform better than those who drank the alcoholic drink by itself. And both groups showed similar impairments in a visual test that challenged them to push buttons in response to a flashing signal on a screen.

The researchers say that young adults should understand that drinking energy drinks with alcohol may impair their judgment, because they perceive themselves to be less affected by the alcohol. "They should drink with more caution, that's the suggestion," says Roseli Boerngen de Lacerda, who studies substance misuse at the Federal University of Paraná in Curitiba, Brazil.