Experts say there's little proof they do anything that coffee doesn't.
From The New York Times…
The drinks are now under scrutiny by the Food and Drug Administration after reports of deaths and serious injuries that may be linked to their high caffeine levels. But however that review ends, one thing is clear, interviews with researchers and a review of scientific studies show: the energy drink industry is based on a brew of ingredients that, apart from caffeine, have little, if any benefit for consumers.
The article says while the drinks have nutrients in concentrations sometimes thousands of times more than the body requires, they are basically about caffeine. Coffee has the same effect, they say, and Starbucks is cheaper than energy drinks.