Energy drinks are widely promoted as products that increase alertness and enhance physical and mental performance. Marketing targeted at young people has been quite effective. Next to multivitamins, energy drinks are the most popular dietary supplement consumed by American teens and young adults. Males between the ages of 18 and 34 years consume the most energy drinks, and almost one-third of teens between 12 and 17 years drink them regularly. Caffeine is the major ingredient in most energy drinks—a 24-oz energy drink may contain as much as 500 mg of caffeine (similar to that in four or five cups of coffee). Energy drinks also may contain guarana (another source of caffeine sometimes called Brazilian cocoa), sugars, taurine, ginseng, B vitamins, glucuronolactone, yohimbe, carnitine, and bitter orange. Consuming energy drinks also increases important safety concerns. Between 2007 and 2011, the overall number of energy-drink related visits to emergency departments doubled, with the most significant increase (279 percent) in people aged 40 and older. A growing trend among young adults and teens is mixing energy drinks with alcohol. About 25 percent of college students consume alcohol with energy drinks, and they binge-drink significantly more often than students who don’t mix them. In 2011, 42 percent of all energy-drink related emergency department visits involved combining these beverages with alcohol or drugs (including illicit drugs, like marijuana, as well as central nervous system stimulants, like Ritalin or Adderall).

Bottom Line:

• Although there’s very limited data that caffeine-containing energy drinks may temporarily improve alertness and physical endurance, evidence that they enhance strength or power is lacking. More important, they can be dangerous because large amounts of caffeine may cause serious heart rhythm, blood flow, and blood pressure problems.
• There’s not enough evidence to determine the effects of additives other than caffeine in energy drinks.
• The amounts of caffeine in energy drinks vary widely, and the actual caffeine content may not be identified easily.

Safety:

• Large amounts of caffeine may cause serious heart and blood vessel problems such as heart rhythm disturbances and increases in heart rate and blood pressure. Caffeine also may harm children’s still-developing cardiovascular and nervous systems.
• Caffeine use may be associated with palpitations, anxiety, sleep problems, digestive problems, elevated blood pressure, and dehydration.
• Guarana, commonly added to energy drinks, contains caffeine. Therefore, the addition of guarana increases the drink’s total caffeine content.
• Young adults who combine caffeinated drinks with alcohol may not be able to tell how intoxicated they are.
• Excessive energy drink consumption may disrupt teens’ sleep patterns and may fuel risk-taking behavior.
• Many energy drinks contain as much as 25–50 g of simple sugars; this may be problematic for people who are diabetic or prediabetic.

http://nccam.nih.gov/health/energy-drink