Sugar content in energy drinks vary by brand, but sometimes can be as high as 30 grams of sugar per serving (that's about six teaspoons of sugar). Remember to look at the label to determine if the brand being used contains one or two servings per container. If it says two servings and you drink the whole can, you will have consumed twice what's on the label.
Unfortunately, the amount of caffeine found in some of these products can also be high, sometimes equivalent to two or three cups of coffee per serving. An average eight-ounce cup of coffee has approximately 80-130mg of caffeine. Most caffeine-containing sodas have between 34-55mg of caffeine per 12 ounces. The caffeine content of most energy drinks can range from 80-300 per eight-ounce serving.
Caffeine can help improve alertness, but caffeine may also increase anxiety, increase nervousness, speed the heart rate, raise blood pressure, and affect one's sleep. Caffeine is dose dependent. A little may be tolerated fine in healthy adults, but may cause adverse side effects in large amounts. Caffeine guidelines for healthy adults are less than 400mg caffeine per day.
Adolescents should have less than 100mg of caffeine per day, if any at all. Children in particular, because of their small body size, could have significant reactions to caffeine, and therefore, it is not recommended at all. Other people who should avoid caffeine are pregnant or nursing women and people with certain heart conditions.