A variety of energy drinks are available; the skinny "bullet" can shape is popular. File:Reloadice adjusted.jpg|256px|right|thumb|Energy drinks are also sold in larger cans and resealable bottles (Reload). Energy drinks are soft drinks advertised as providing energy to improve physical activity of the drinker, as compared to a typical drink. Rather than providing food energy (as measured in calories), these drinks are designed to increase a user's mental alertness and physical performance by the addition of caffeine, vitamins, and herbal supplements which may interact to provide a stimulant effect over and above that obtained from caffeine alone.

Ingredients

Generally energy drinks include methylxanthines (including caffeine), vitamin B and herbs. Other common ingredients are guarana, which has a high caffeine content, and taurine, plus various forms of ginseng, maltodextrin, carbonated water, inositol, carnitine, creatine, glucuronolactone and ginkgo biloba. Some contain high levels of sugar, and many brands also offer artificially-sweetened 'diet' versions. The central ingredient in most energy drinks is caffeine, the same stimulant found in coffee or tea, often in the form of guarana or yerba mate. also there is a myth that the ingredient (TAURINE) in most energy drinks comes from the testicles of a bull.

The average 237 milliliter (8 fluid ounce) energy drink has about 80 mg of caffeine, with 480 mL (16 fl. oz.) drinks containing around 150 mg.

Desirable effects

A variety of physiological and psychological effects attributed to energy drinks and/or their ingredients have been investigated.

Two studies reported significant improvements in mental and cognitive performances as well as increased subjective alertness. Excess consumption of energy drinks may induce mild to moderate euphoria primarily caused by stimulant properties of caffeine and may also induce agitation, anxiety, irritability and insomnia. During repeated cycling tests in young healthy adults an energy drink significantly increased upper body muscle endurance. It was also suggested that reversal of caffeine withdrawal is a major component of the effects of caffeine on mood and performance.

Restorative properties were shown by a combination of caffeine and CHO in an energy drink, and some degree of synergy between the cognition-modulating effects of glucose and caffeine was also suggested. In one experiment, a glucose-based energy drink (containing caffeine, taurine and glucuronolactone) was given to eleven tired participants being tested in a driving simulator. Lane drifting and reaction times were measured for two hours post-treatment and showed significant improvement.

Two articles concluded that the improved information processing and other effects could not be explained in terms of the restoration of plasma caffeine levels to normal following caffeine withdrawal.

Adverse effects

Caution is warranted even for healthy adults who choose to consume energy beverages. Consumption of a single energy beverage will not lead to excessive caffeine intake; however, consumption of two or more beverages in a single day can. Other stimulants such as ginseng are often added to energy beverages and may enhance the effects of caffeine,Fact: date=September 2008 and ingredients such as guarana themselves contain caffeine. Adverse effects associated with caffeine consumption in amounts greater than 400 mg include nervousness, irritability, sleeplessness, increased urination, abnormal heart rhythms (arrhythmia), and stomach upset. The concentration of sugar in a sports drink is recommended to be 6-7% carbohydrate to allow maximum absorption and minimize spikes and crashes in blood sugar. Higher concentrations such as those seen in energy drinks will slow fluid absorption into the blood and energy system, increasing the possibility of dehydration. When a high level of sugar is in the blood stream the body cannot get the water into the cells that it needs because the water is busy trying to dilute concentration of sugar in the blood stream. The actual number of people suffering from adverse effects is difficult to measure since many cases go unreported.