1. Introduction

Energy drinks are one of the most popular packaged beverage products consumed within the United States (US). These products are considered a functional beverage, a category that also includes sports drinks and nutraceutical beverages [1]. Recently, annual energy drink sales have experienced tremendous growth, with estimated sales amounting to USD 2.8 billion in 2015 and sales up to USD 12 billion in 2020 (bevindustry.com, accessed on 15 September 2021). Energy drinks are commonly marketed to consumers with purported benefits of increased energy and alertness; reduced sensations of fatigue; enhanced physical performance; increased metabolic activity; and a plethora of other physiological, metabolic, cognitive, and performance benefits [2]. These ready-to-drink beverages often come in serving sizes of 8-16 oz. with 1-2 servings commonly found in a pre-packaged can and typically contain a combination of caffeine, vitamins, amino acids, electrolytes, and herbal extracts. Zero-calorie or sugar-free versions of each drink are commonly available commercially [2]. Similarly, energy “shots” are another commonly consumed pre-packaged beverage offering a similar ingredient profile, albeit in condensed versions, often with serving sizes of 3 oz. Historically, energy drinks first emerged to the market within the US in the late 1990s. Initially marketed towards young, active adults, these drinks are now regularly consumed by adolescents, young and older adults [3], athletes [4], and military personnel [5], with consumption rates tending to be higher in males compared with females [3]. While the prevalence of energy drink consumption has increased steadily in young adults from 0.5% to 5.5% during the span of 2003-2016, this consumption rate is still far below that of coffee, another popular caffeinated beverage, in which over half of the US population regularly consumes on a daily basis (mean intake: 54 g per day (~2.5 cups)), making up a majority of their daily caffeine intake and equating to a mean caffeine intake of 233 mg per day [6]. Comparatively, the United States Food and Drug Administration (FDA) states that amounts up to 400-600 mg per day appear to be safe for consumption, without any evidence of adverse effects when consumed below this threshold, whereas rapid ingestion of 1200 mg of caffeine appears to the upper end of the threshold for toxic effects, such as seizures or cardiovascular complications [7].

With the high caffeine content in certain energy drinks, in addition to the combination of varied ingredients, there have been concerns regarding both the acute and long-term safety of consuming these products. A growing number of case reports and clinical trials identifying various adverse effects following acute ingestion of energy drinks, namely acute hemodynamic perturbations, disturbances in vascular function, and other cardiovascular abnormalities, particularly when consumed in excess, have been reported [8,9,10,11,12,13]. Moreover, on a population level, it has been demonstrated that caffeine-containing products (such as energy drinks and shots) are associated with a higher risk of severe adverse events compared with non-caffeine containing products [14]. Furthermore, there have been reports of regular energy drink consumption being associated with sleep disturbances [15], anxiety [16], and substance abuse issues [17,18]. However, more work is needed to identify the exact mechanisms and whether the high caffeine content; combination of (and potentially excessive concentration of) vitamins, amino acids, and herbal extracts; or all of the above are contributors to the safety concerns and potential for cardiovascular-related adverse events.

Collectively, the consumption rates and popularity of these beverages are on the rise, and therefore, it is important to continue examining the prevalence of use as well as the acute and long-term effects of regularly consuming these products. More importantly, it is imperative to first establish a definition and a common ingredient profile to help provide context for when these products are included in future research activities or in conversations regarding the development of any policies, regulations, and guidance for use. Therefore, the focus of the current study was to examine the nutrition fact panels of the top selling commercially available energy drink and energy shot products within the US to help establish a standard definition and ingredient profile of energy drinks and energy shots for consumers, health care practitioners, and researchers.