A recent study making the news today, warns about the risks of energy drinks. 30-50% of adolescents and young adults drink them, they have lots of caffeine and other additives, and they do not have a whole lot of benefits.
Energy drinks have no therapeutic benefit, and many ingredients are understudied and not regulated. The known and unknown pharmacology of agents included in such drinks, combined with reports of toxicity, raises concern for potentially serious adverse effects in association with energy-drink use.
–Sara Seifert et al., 2011: Health Effects of Energy Drinks on Children, Adolescents, and Young Adults
Applying the precautionary principle might be in order.