Combining alcohol with caffeinated energy drinks increases the risk of injury, warns a Canadian review of 13 studies, published in the Journal of Studies on Alcohol and Drugs. The practice has become so common across North America, it has its own acronym (AmED, for Alcohol mixed with Energy Drinks)—but it’s a bad mix.
The problem is that users underestimate how intoxicated they become because stimulants in the energy drinks mask the sedative effects of the alcohol, creating an “awake drunk” state of mind and likely a much higher risk of injury relative to the use of each substance alone.
Though most commercial premixed drinks, such as Four Loko and Rockstar 21, have been discontinued or reformulated since the FDA told several companies to stop selling them in 2010, many people combine alcohol and caffeine on their own, and some craft beers still contain the combination.
The CDC also warns about this dangerous combo, cautioning that "Drinkers who mix alcohol with energy drinks are more likely than drinkers who do not mix alcohol with energy drinks to report unwanted or unprotected sex, driving drunk or riding with a driver who was intoxicated, or sustaining alcohol-related injuries."
Also see Caffeine in Energy Drinks.