Review
Caffeinated energy drinks—A growing problem

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Abstract

Since the introduction of Red Bull in Austria in 1987 and in the United States in 1997, the energy drink market has grown exponentially. Hundreds of different brands are now marketed, with caffeine content ranging from a modest 50 mg to an alarming 505 mg per can or bottle. Regulation of energy drinks, including content labeling and health warnings differs across countries, with some of the most lax regulatory requirements in the U.S. The absence of regulatory oversight has resulted in aggressive marketing of energy drinks, targeted primarily toward young males, for psychoactive, performance-enhancing and stimulant drug effects. There are increasing reports of caffeine intoxication from energy drinks, and it seems likely that problems with caffeine dependence and withdrawal will also increase. In children and adolescents who are not habitual caffeine users, vulnerability to caffeine intoxication may be markedly increased due to an absence of pharmacological tolerance. Genetic factors may also contribute to an individual's vulnerability to caffeine-related disorders including caffeine intoxication, dependence, and withdrawal. The combined use of caffeine and alcohol is increasing sharply, and studies suggest that such combined use may increase the rate of alcohol-related injury. Several studies suggest that energy drinks may serve as a gateway to other forms of drug dependence. Regulatory implications concerning labeling and advertising, and the clinical implications for children and adolescents are discussed.

Introduction

In 2006, annual worldwide energy drink consumption increased 17% from the previous year to 906 million gallons, with Thailand leading the world in energy drink consumption per person, but the U.S. leading the world in total volume sales (Zenith International, 2007). Although “energy drinks” first appeared in Europe and Asia in the 1960s, the introduction of “Red Bull” in Austria in 1987 and in the U.S. in 1997 sparked the more recent trend toward aggressive marketing of high caffeine content “energy drinks”. Since its inception, the energy drink market has grown exponentially, with nearly 500 new brands launched worldwide in 2006 (Johnson, 2006), and 200 new brands launched in the U.S. in the 12-month period ending July 2007 (Packaged Facts, 2007). From 2002 to 2006, the average annual growth rate in energy drink sales was 55% (Packaged Facts, 2007) (Fig. 1). The total U.S. retail market value for energy drinks (from all sources) was estimated to be $5.4 billion in 2006 and has shown a similar annual growth rate over this same period (47%) (Packaged Facts, 2007). These drinks vary widely in both caffeine content (ranging from 50 to 505 mg per can or bottle) and caffeine concentration (ranging from 2.5 to 171 mg per fluid ounce) (Table 1). For comparison, the caffeine content of a 6 oz cup of brewed coffee varies from 77 to 150 mg (Griffiths et al., 2003). The main active ingredient in energy drinks is caffeine, although other substances such as taurine, riboflavin, pyridoxine, nicotinamide, other B vitamins, and various herbal derivatives are also present (Aranda and Morlock, 2006). The acute and long-term effects resulting from excessive and chronic consumption of these additives alone and in combination with caffeine are not fully known. Although the full impact of the rise in popularity of energy drinks has yet to be realized, the potential for adverse health consequences should be considered and may be cause for preemptive regulatory action.

Section snippets

Regulatory aspects

The regulation of beverages to which caffeine is added has been challenging, partly because of the widespread and long-term use of beverages such as coffee and tea in which caffeine is a natural constituent. Nonetheless, several countries have enacted measures to regulate the labeling, distribution, and sale of energy drinks that contain significant quantities of caffeine. The European Union requires that energy drinks have a “high caffeine content” label (European Union, 2007) and Canada

Advertising

Energy drinks are promoted for their stimulant effects and claim to offer a variety of benefits including increased attention, endurance and performance, weight loss, and “having fun, kicking butt and making a difference” (Bookoo website, 2008). The majority of these claims however, remain to be substantiated. The most consistent result to emerge is that caffeine reduces performance decrements due to reduced alertness (e.g. conditions of fatigue, or sleep deprivation) (Bonnet et al., 2005).

Caffeine toxicity/overdose

Concern regarding the caffeine content of energy drinks is prompted by the potential adverse consequences of caffeine use. One such adverse effect is caffeine intoxication, a recognized clinical syndrome included in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) and the World Health Organization's International Classification of Diseases (ICD-10) (American Psychiatric Association, 1994, World Health Organization, 1992a, World Health Organization, 1992b). Caffeine toxicity

Caffeine dependence

The DSM-IV-TR defines substance dependence using a generic set of cognitive, physiological, and behavioral symptoms, including the inability to quit, use despite harm, using more than intended, withdrawal, and tolerance. Although DSM-IV-TR specifically excludes caffeine from its diagnostic schema for substance dependence, the World Health Organization's International Classification of Diseases (ICD-10) includes this diagnosis (World Health Organization, 1992a, World Health Organization, 1992b).

Caffeine withdrawal

Symptoms of caffeine withdrawal have been described in the medical literature for more than a century (Griffiths and Woodson, 1988). There have been at least 66 studies of caffeine withdrawal in the medical literature, the majority of which have been published within the last 10 years (Juliano and Griffiths, 2004). The symptoms of caffeine withdrawal, the most common of which is headache, begin 12–24 h after the last dose of caffeine (Driesbach and Pfeiffer, 1943, Lader et al., 1996, Juliano and

Combined use of caffeine and alcohol may be problematic

There is an association between the heavy use of caffeine and the heavy use of alcohol (Istvan and Matarazzo, 1984, Kozlowski et al., 1993), and the ingestion of energy drinks in combination with alcohol is becoming increasingly popular (O’Brien et al., 2008, Oteri et al., 2007), with 24% of a large stratified sample of college students reporting such consumption within the past 30 days (O’Brien et al., 2008). In the previously mentioned survey of 496 college students, 27% reported mixing

Relationship of caffeine to dependence on other substances

Studies in adult twins show that lifetime caffeine intake, caffeine toxicity and caffeine dependence are significantly and positively associated with various psychiatric disorders including major depression, generalized anxiety disorder, panic disorder, antisocial personality disorder, alcohol dependence, and cannabis and cocaine abuse/dependence (Kendler et al., 2006). Studies in adult twins examining caffeine use, alcohol use, and cigarette smoking concluded that a common genetic factor

Vulnerability to caffeine affected by tolerance and genetic factors

Vulnerability to caffeine intoxication after bolus caffeine doses, such as those delivered in energy drinks, is markedly affected by pharmacological tolerance. Tolerance refers to a decrease in responsiveness to a drug as a result of drug exposure. Daily administration of very high doses of caffeine (e.g. 750–1200 mg/day) can produce complete or partial tolerance to caffeine's subjective, pressor, and neuroendocrine effects (Robertson et al., 1981, Evans and Griffiths, 1992, Griffiths and

Conclusions and implications

The consumption of high caffeine content energy drinks has increased markedly in recent years. Regulation of energy drinks, including content labeling and health warnings has differed across countries, with among the most lax regulatory requirements in the U.S., which is also the largest market for these products. The absence of regulatory oversight has resulted in aggressive marketing of energy drinks, targeted primarily toward young males, for psychoactive, performance-enhancing and stimulant

Conflict of interest

Dr Reissig owns stock in PepsiCo Corporation. Dr Strain owns stock in Starbucks and PepsiCo Corporations, is an investigator on several grants from the National Institute on Drug Abuse (NIDA), and has been a consultant to various pharmaceutical companies on issues about drug abuse liability. Dr Griffiths owns a single share of stock from the Coca-Cola Company, and is an investigator on grants or contracts from NIDA, the Council on Spiritual Practices, the Heffter Research Institute, and the

Acknowledgements

The authors thank Dr Michael Jacobson and Ilene Heller, JD at Center for Science in the Public Interest for helpful comments about federal regulation of caffeine.

Role of Funding Source: Conduct of the study was supported by grants R01 DA03890 and K24 DA023186 from the National Institute on Drug Abuse.

Contributors: All authors contributed equally to the preparation and review of the manuscript. All authors have approved the final manuscript.

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