Energy drinks work primarily by distributing a large amount of caffeine to the central nervous system which gives the drinker a greater feeling of alertness. Taurine increases oxygen flow to the cells, lessens muscle contractions and regulates heartbeat and energy levels. Guarana provides additional caffeine and increases alertness and energy levels.
Other active ingredients in energy drinks include B vitamins, sugar, ginseng and L-carnitine. Both ginseng and L-carnitine help to increase energy levels. L-carnitine helps to increase endurance and metabolism. Ginseng helps to improve memory function and may help to relieve stress.
Sugar turns into glucose, which turns into energy. It gives the body additional carbohydrates that are turned into fuel. The large amount of sugar in many energy drinks causes insulin levels to increase rapidly which can cause a rush of energy followed by a "crash," or sudden drop in energy.
B vitamins are used by the body to convert food and drink into energy. Because B vitamins that are consumed orally do not absorb well in the body, drinking them in the form of an energy drink may do little to increase energy levels and alertness.
The most active ingredient in most energy drinks is caffeine. Typical energy drinks have between 70 and 200 milligrams of caffeine, while the average cup of percolated coffee contains 65 to 125 milligrams of caffeine.