Energy drinks like Red Bull and Monster Energy have a number of serious health concerns, both real (traces of cocaine?) and potential. Two recent reviews have covered the topic in great detail and are worth a read if you are interested in the science behind these drinks and their true risks. The evidence is not strong, mostly just theoretical and case reports, but these papers represent the sum of our current scientific knowledge (aside from any proprietary information held by the companies that produce them.)
The first review is in the November 2010 issue of Mayo Clinic Proceedings, by Dr. Higgins and colleagues (free full text from Mayo Clinic Proceedings is usually available six months after publication). These authors review research on energy drinks, but also dissect out information on many of the components and ingredients. The second review is in Pediatrics and authors by Dr. Seifert and colleagues and their review is available for free, now. This review focuses on caffeine content providing information about lethality of caffeine and comparing the content in energy drinks to other foods and drinks.