Energy Drinks to Improve Performance

By Dónal P. O’Mathúna, BS (Pharm), MA, PhD, Senior Lecturer, Ethics, Decision-Making & Evidence, School of Nursing, Dublin City University, Ireland. Dr. O’Mathúna reports no financial relationships relevant to this field of study.

Energy drinks have rapidly become very popular, especially among adolescents and young adults. Recent trends can be traced to the introduction of Red Bull in Austria in 1987 and the United States in 1997.1 Hundreds of brands are now available, with sales increasing exponentially. Six billion energy drinks were sold in the United States in 2010, up from 2.3 billion in 2005.2 They are most commonly consumed to counteract tiredness, increase energy, and maintain alertness for driving or studying.3 Highly concentrated products are now available as “energy shots” and “energy sheets” which dissolve on the tongue.2 Energy drinks also are consumed with alcohol to enhance its intoxicant effects, and then afterward to relieve hangovers.2

The primary ingredients in energy drinks are caffeine, taurine, and simple sugars (like sucrose, fructose, or beet sugar).3 Guarana (Paulinia cupana) from South America often is added as it provides about 250 mg caffeine per 3-5 g herb (see Table for comparison with other caffeine sources).4 Guarana contains other compounds related to caffeine with similar effects, so its addition is not equivalent to adding more caffeine. A variety of herbs and other compounds are contained in specific brands, including Gingko biloba, Panax ginseng, L-carnitine, and B vitamins.2 The actual ingredients, and their amounts, vary widely (see Table).

Energy drinks will be distinguished here from sports drinks that contain primarily glucose and electrolytes and are consumed to counteract dehydration, improve muscle function, and decrease exercise-related exhaustion. Both drinks are used by athletes, but energy drinks are distinguished by their high caffeine levels. Health care professionals should be aware of the effects of energy drinks because of their widespread consumption, especially among young males, and growing concerns about the adverse effects of their over-consumption.


Caffeine is the most widely used stimulant in the world, and is generally recognized as safe. About 90% of adults drink caffeinated beverages, with an average daily intake of 227 mg caffeine.6 What is new with energy drinks is the amount of caffeine being consumed by adolescents, and how it is being consumed with other substances.7 Energy drink marketing specifically targets adolescents and young adults through its catchy slogans and sponsorship of extreme sports and high-risk activities.6

Regulation of energy drinks varies widely. Some countries ban all energy drinks (like Uruguay), restrict their sale to pharmacies (like Norway), or limit their caffeine content.8 Some European countries initially banned Red Bull, but these bans were overturned and applicable energy drinks must now carry a “high caffeine content” label.1 In Canada, labels must include warnings, a maximum daily consumption, and caution against mixing energy drinks with alcohol.8

Regulation of energy drinks in the United States has been complicated. Historically, caffeinated beverages were regulated by the FDA as foods.1 In 1980, the FDA proposed eliminating caffeine from such drinks because of concerns about its health effects. Soft drink manufacturers responded that caffeine was a flavor enhancer and the FDA introduced a maximum caffeine content of 0.02% or 71 mg per 12 oz container for soft drinks.

Many energy drinks exceed the FDA limit, but sanctions are avoided by using the 1994 Dietary Supplement Health and Education Act. The drinks can be classified as dietary supplements because they contain herbs and other natural products.1 Thus, an over-the-counter medication like NoDoz (containing 100 mg caffeine per tablet) must include several warnings on its label, while an energy drink containing more than 500 mg caffeine carries no information or warnings. However, premixed alcoholic drinks containing caffeine were effectively banned in 2010 when the FDA declared caffeine an “unsafe food additive” in alcoholic beverages.2

Mechanism of Action

Caffeine is a central and peripheral nervous system stimulant, which antagonizes adenosine receptors and potentiates dopamine neurotransmission.6 Interactions with different receptors lead to numerous effects. In adults, moderate acute doses (200-350 mg) decrease heart rate and increase blood pressure, while also enhancing feelings of well-being, improving concentration, and increasing arousal.7 At higher doses (> 400 mg), feelings of anxiety, nervousness, and jitteriness predominate. Little research has focused on children and adolescents, but similar effects have been observed, except that negative effects have been observed in children (13-17 years) after 100 mg.

Taurine is an organic acid that is found throughout the body, especially within the central nervous system. Because of its role in healthy development, it has been added to infant formula since the 1980s.8 Taurine has many roles, and is essential for cardiovascular functioning and in skeletal muscle. Although many popular energy drinks contain 1-2 g/serving, its role is unclear.3 Claims are made that it promotes energy utilization and exercise performance, but these are based on studies involving taurine combined with other ingredients. A study of 11 male endurance cyclists found no performance improvement with 1.66 g taurine, while total fat oxidation increased 16% compared to placebo (P < 0.05).9

Simple sugars are a rapidly absorbed source of energy and are added to energy drinks for this reason and to improve cognitive performance. Drinks typically contain about 27 g sugar per 8 oz.3 Larger volume energy drinks exceed the maximum recommended daily intake of 32 g sugar.4

Table. Caffeine Content of a Representative Sample of Caffeinated Beverages1,5


Clinical Studies

Individual energy drinks constituents will be discussed first. The best-researched of these is caffeine, with several studies showing it counteracts poor performance due to reduced alertness, increases long-term exercise endurance, and improves speed and power output.7 Age-related differences in caffeine’s effects have been identified. One study involved 26 boys and 26 men given a 5 mg/kg caffeinated drink.10 No differences were found in either group for blood pressure or exercise performance. However, heart rate was significantly lower for the boys at rest and during exercise, while no changes occurred in the men. Other studies have found age-related differences in caffeine’s cognitive effects, such as boys showing greater reduction in reaction time than men and greater increases in speech rates.8

Almost all the research on taurine has been conducted with animals. Studies found that when animals are given neurotoxins, taurine prevents or reverses resulting deficits in learning and memory, but does not enhance cognitive performance in healthy animals.3 A 2012 review found no human studies of taurine’s influence on caffeine-induced changes in cognitive performance.

The effect of simple sugars on cognition has produced inconsistent results. A systematic review identified about 30 clinical trials, most examining memory.11 Among these, about half found some beneficial effects but the other half did not. Positive findings were more consistently found with elderly subjects, with little impact on younger subjects. Four studies examined mood, with increased vigilance and decreased fatigue identified in one study each, while two other studies found no significant impact on mood. Glucose’s cognitive effects in combination with caffeine have been studied in three trials. Two showed reduced reaction time and improved attention and memory, while one showed no impact on attention.3

Relatively few randomized controlled trials (RCTs) have been published on energy drinks. In one, 20 undergraduate students (mean age 21 years) participated in a 5-way crossover study.12 They consumed 250 mL containing either 37.5 g glucose, 75 mg caffeine, ginseng, and gingko as flavorants (not intended to have physiological effects), the energy drink (glucose, caffeine, ginseng, and gingko), or a placebo consisting of the vehicle used for the other drinks. Compared to placebo, the energy drink significantly improved “secondary memory” (P = 0.007) and “speed of attention” (P = 0.044), but no other cognitive measures, mood, or heart rate. No significant changes in cognitive factors were found with any of the individual components.

A double-blind RCT was conducted with 81 subjects undergoing firefighter training.13 Each received a 330 mL drink containing either 50 g glucose and 40 mg caffeine, 10.25 g fructose/glucose and 80 mg caffeine, or placebo (no details given on its composition or taste). Several cognitive, mood, and performance measures were used. Both energy drinks resulted in significant improvements in information-processing tasks (P = 0.039), while the 50 g glucose plus 40 mg caffeine drink showed improved grip strength (P = 0.01) and memory (P < 0.05), and decreased anxiety (P = 0.038) and self-reported stress levels (P < 0.05).

One article reported on three small studies involving Red Bull energy drink and sports performance.14 Whether the study was sponsored by Red Bull was not mentioned. Each study involved 10-14 undergraduate students (mean ages 20-24 years). Participants drank either Red Bull or a placebo drink. The Red Bull groups improved aerobic endurance by 9% (P < 0.05) and anaerobic performance by up to 24% (P < 0.05). Significant improvements also occurred in mental performance, including choice reaction time, concentration, and memory.

Red Bull sponsored an RCT that examined the effect of Red Bull on driving performance in 24 adults (mean age 22.8 years).15 Subjects drove for 2 hours on a simulator that monitored weaving and speed. During a 15-minute break, participants consumed 250 mL of either Red Bull or placebo Red Bull made by the manufacturer. They drove for another 2 hours. Driving quality, mental effort, and sleepiness also were measured subjectively. When authentic Red Bull was consumed, significant reductions in weaving and sleepiness were found during the third and fourth hours of driving. During the third hour only, improvements were found in speed consistency, subjective driving quality, and mental effort.

Adverse Effects

One energy drink taken by an adult appears to be safe. However, many reports raise concerns about the over-consumption of energy drinks, mixing them with alcohol, and their use by adolescents. Case reports are linked to concerns about caffeine toxicity. Case studies reporting adverse effects typically involve large volumes of energy drinks, such as atrial fibrillation after 575 mg caffeine daily, acute hepatitis after 10 cans per day, jaundice after several cans, five cases of epilepsy after at least 480 mg caffeine, and severe anxiety after 6-8 energy drinks per day.2 Australian poison control centers reported 12 energy drink-related cases in 2004, which increased to 65 in 2010.16 These patients had an average age of 17 years, with a median consumption of 5 units per session. The most common symptoms were palpitations, agitation, tremor, and gastrointestinal upset, but serious cardiac and neurological effects also were reported, with more than half requiring hospitalization.

The manufacturers of Monster Energy Drink were sued in October 2012 following the death of a 14-year-old girl. She consumed two 24 oz cans of Monster in the 24 hours before her death and the autopsy report attributed her death to “cardiac arrhythmia due to caffeine toxicity.”17 Following this, the FDA stated they were investigating reports that Monster was linked to five deaths, and reports of 13 deaths associated with 5-Hour Energy, a concentrated energy shot.

Concerns also exist about the use of energy drinks along with other substances. The Australian report found that in almost half the cases involving energy drinks, patients had consumed other substances, usually other caffeinated products or alcohol.16 Numerous studies have identified higher rates of alcohol-related harm (such as being taken advantage of sexually, driving under the influence, or being injured) when people consume large quantities of alcohol mixed with energy drinks.18 Compared to alcohol alone, alcohol plus energy drinks increased self-reported sense of stimulation, counteracted some alcohol-related impairments, but did not change inhibition nor ability to drive.19 Numerous cases of intoxicated young adults requiring emergency room treatment have been published where energy drinks were involved. The average age of those involved in one case series was 16 years.20


Energy drinks increase alertness and may improve physical performance. They serve as stimulants like others drink tea or coffee. They are the subject of intensive marketing, especially to younger people. The resulting increased consumption of caffeine by adolescents has unknown consequences. Over-consumption of energy drinks puts people at risk of caffeine toxicity, although the level at which this occurs varies individually and with age. Combined with alcohol, they place people at higher risk of intoxication and many adverse effects. Other indirect concerns are raised about energy drinks because consumption of caffeine-containing beverages in children is associated with greater BMI, greater intake of unhealthy foods, and lower intake of fruits and vegetables.7


Many people are consuming more caffeine younger, and health care professionals should be alert to symptoms of caffeine toxicity, especially in adolescents and young adults. There should be an increase in education on the risks of overconsumption of energy drinks and the dangers of mixing them with alcohol. The long-term effects of regular consumption of energy drinks are not known. Chronic use of any stimulant is not an adequate replacement for adequate rest and sleep. As with most areas, moderation should be encouraged. For most healthy adults, 200-300 mg caffeine per day is not harmful, whether obtained from coffee or energy drinks. For adolescents, the tolerable amount is lower, but evidence for clear guidance is lacking. What is clear is that energy drinks and alcohol are an unsafe combination, especially for adolescents.


1. Reissig CJ, et al. Caffeinated energy drinks—A growing problem. Drug Alcohol Depend 2009;99:1-10.

2. Wolk BJ, et al. Toxicity of energy drinks. Curr Opin Pediatr 2012;24:243-251.

3. Giles GE, et al. Differential cognitive effects of energy drink ingredients: Caffeine, taurine, and glucose. Pharmacol Biochem Behav 2012;102:569-577.

4. Rath M. Energy drinks: What is all the hype? The dangers of energy drink consumption. J Am Acad Nurse Pract 2012;24:70-76.

5. Center for Science in the Public Interest. Caffeine content of food & drugs. 2007.

6. Temple JL. Caffeine use in children: What we know, what we have left to learn, and why we should worry. Neurosci Biobehav Rev 2009;33:793-806.

7. Temple JL, et al. Effects of acute caffeine administration on adolescents. Exp Clin Psychopharmacol 2010;18:510-520.

8. Seifert SM, et al. Health effects of energy drinks on children, adolescents, and young adults. Pediatrics 2011;127:511-528.

9. Rutherford JA, et al. The effect of acute taurine ingestion on endurance performance and metabolism in well-trained cyclists. Int J Sport Nutr Exerc Metab 2010;20:322-329.

10. Turley KR, et al. Effects of caffeine on physiological responses to exercise: Boys versus men. Pediatr Exerc Sci 2007;19:481-492.

11. Gorby HE, et al. Do specific dietary constituents and supplements affect mental energy? Review of the evidence. Nutr Rev 2010;68:697-718.

12. Scholey AB, Kennedy DO. Cognitive and physiological effects of an “energy drink”: An evaluation of the whole drink and of glucose, caffeine and herbal flavouring fractions. Psychopharmacol 2004;176:320-330.

13. Sünram-Lea SI, et al. The effect of energy drinks on cortisol levels, cognition and mood during a fire-fighting exercise. Psychopharmacol 2012;219:83-97.

14. Alford C, et al. The effects of red bull energy drink on human performance and mood. Amino Acids 2001;21:139-150.

15. Mets MA, et al. Positive effects of Red Bull® Energy Drink on driving performance during prolonged driving. Psychopharmacol 2011;214:737-745.

16. Gunja N, Brown JA. Energy drinks: Health risks and toxicity. Med J Aust 2012;196:46-49.

17. Fox M. FDA investigating energy drinks after deaths, paper reports. NBC News. Available at: Accessed Nov. 15, 2012.

18. Wells BE, et al. Correlates of concurrent energy drink and alcohol use among socially active adults. Am J Drug Alcohol Abuse 2012 Oct 3. [Epub ahead of print].

19. Marczinski CA, et al. Mixing an energy drink with an alcoholic beverage increases motivation for more alcohol in college students. Alcohol Clin Exp Res 2012 Jun 22. [Epub ahead of print].

20. Cleary K, et al. Adolescents and young adults presenting to the emergency department intoxicated from a caffeinated alcoholic beverage: A case series. Ann Emerg Med 2012;59:67-69.