In this study of fourth-year college students at one large public university, energy drinks were consumed by nearly two-thirds of students (61.4%wt) at some time in the past year, and 10.1%wt consumed these drinks on a weekly or daily basis. These high-frequency energy drink users had significantly heavier alcohol involvement, including drinking more often, drinking more heavily on days they drank, and having greater risk for alcohol-related problems such as blackouts, hangover-related impairments, and meeting DSM-IV criteria for alcohol dependence. Furthermore, multivariate analyses revealed that high-frequency energy drink users were twice as likely as low-frequency users—and more than twice as likely as non-users—to meet criteria for alcohol dependence, independent of demographics, typical quantity of alcohol consumed, fraternity/sorority involvement, depressive symptoms, parental history of alcohol/drug problems, and childhood conduct problems.
The present findings support and extend prior evidence that energy drink users are at increased risk for substance use problems (Miller, 2008a
). To our knowledge, this study contributes new information regarding the association between energy drink consumption and alcohol dependence, and results support the expected dose-response relationship between energy drink consumption and heavy drinking. Specifically, high-frequency energy drink users were at increased risk for alcohol dependence, independent of several other risk factors. While low frequency consumption was not independently associated with increased risk for alcohol dependence, low frequency users experienced several more alcohol-related problems than non-users.
While this study confirmed the observations of other investigators (Miller, 2008a
; Miller, 2008b
; O'Brien et al., 2008
) that energy drink users are different from non-users in a number of respects (i.e., higher risk-taking tendencies and substance involvement), it appears that these characteristics do not fully explain the increased risk for alcohol-related problems. Our multivariate analyses confirmed that high-frequency energy drink consumption confers a risk over and above that of these confounding risk factors for alcohol dependence.
However, because the study was cross-sectional, the possibility cannot be ruled out that heavy drinkers rely on energy drinks to help them function normally throughout the day, as a way of compensating for alcohol-related hangover effects. For example, a college student might use energy drinks to get through classes on the day after a drinking binge, and if chronic partying interferes with their study habits they might consume energy drinks to pull “all-nighters” before exams. Future research is needed to clarify the mechanisms by which energy drink consumption might be related to increased risk for alcohol-related problems. For example, whether energy drink use increases the reinforcing effects of alcohol or the disinhibition typically associated with alcohol remains to be seen. Unfortunately, experimental studies might be limited in the extent to which they can model the extremely high levels of alcohol consumption that occur in naturalistic settings. Moreover, it will be important to understand the variety of contexts in which energy drinks are consumed and the differential risks between simultaneous versus concurrent ingestion of alcohol and energy drinks.
The findings must be interpreted in light of several limitations. Self-report studies are always subject to response bias, and while we have no indication that over- or under-reporting has occurred, we cannot rule out this possibility. Second, our measure of caffeine consumption relies on secondary data, albeit from a source we regard as reliable, but we did not conduct our own testing to confirm the caffeine concentrations of different products. Third, although we did not explicitly ask whether or not participants were co-ingesting energy drinks with alcohol, prior research evidence (Malinauskas et al., 2007
; O'Brien et al., 2008
) as well as anecdotal evidence from our participants indicates that consuming mixed drinks containing both alcohol and energy drinks is quite common, especially among high-frequency consumers. Lastly, the study ascertained young adults from one large public university, and thus we cannot generalize the findings to other settings.
This study's strengths include a large sample size and the breadth of domains assessed in this study, which provides a rare opportunity to compare the statistical effect of energy drinks with that of several other important indicators of risk. In many ways college students are an ideal population in which to study the association of energy drinks and alcohol use, due to the popularity therein of both beverages and the high prevalence of alcohol-related problems. Moreover, this study demonstrates a new methodology for measuring energy drink consumption in a more fine-grained manner than prior studies. One unique contribution of this study is the use of an empirically-derived cutpoint characterizing a high-risk pattern of energy drink consumption, on the basis of risk for alcohol dependence. Interestingly, certain other alcohol-related consequences did not correlate as well with this definition of high-risk energy drink consumption, notably drunk driving and personal injury, raising the possibility that lower thresholds might better distinguish energy-drink consumption patterns that confer high risk for these consequences.
In this study we focused our analyses on alcohol dependence rather than alcohol use disorders and chose not to consider alcohol abuse as a main outcome. This decision was made in light of the body of evidence cited by the Substance Use Disorders Workgroup for the development of the DSM-5, which has concluded that the diagnostic distinction between abuse and dependence is questionable and recommends the transition to a single diagnosis of substance use disorder that would be graded according to levels of severity (American Psychiatric Association, 2010
). Not surprisingly, in our sample, there is considerable overlap between individuals meeting criteria for abuse and dependence over time, for example, with 57.5% (data not presented in a table) of our alcohol dependence cases in Year 4 having already met criteria for alcohol abuse in one of the three prior interviews. An examination of all four annual assessments revealed that 41.8% of abuse cases also met dependence criteria at some point. Therefore, we regard alcohol dependence as defined in the DSM-IV (American Psychiatric Association, 1994
) as the more severe manifestation of alcohol use disorder and a more reliable indicator of serious alcohol problems in our sample.
The present findings have important implications for researchers, policymakers, and the general public. Researchers should be aware of the fact that many young adults consume alcohol in the context of energy drinks and should add questions about energy drink consumption to their assessment instruments. Given the mounting public health concern regarding how co-ingestion of energy drinks with alcohol might exacerbate aggressive and dangerous behaviors by creating a state of “wide-awake drunkenness” (Arria and O'Brien, 2009
), more research is needed to understand the nature and extent of this problem.
The present finding that frequent consumption of energy drinks—but not other caffeinated beverages—contributes to increased risk for alcohol dependence adds more urgency for policymakers to adopt and enforce measures that would separate the consumption of these two beverages. If our findings are replicated, labeling of energy drink products that caution against mixing alcohol and energy drinks might be warranted, and vendors could be required to limit sales of energy drinks and cocktails made with them to patrons who are intoxicated.
It is troubling that there are no requirements for disclosing the caffeine content of energy drinks on the product label. We observed considerable variability in how much caffeine users are consuming from different energy drinks, and therefore find it plausible that, when consuming one of the more concentrated energy drinks, some users might be ingesting much more caffeine than they realize. Individuals who typically consume an energy drink with lower caffeine content might inadvertently ingest more caffeine than intended if under the incorrect assumption that they are “all the same.” We strongly encourage policymakers to require explicit labeling of energy drinks, so that consumers can have accurate information regarding caffeine content.
Lastly, with respect to the general public, parents and peers could play a valuable role in monitoring risk for alcohol related consequences among energy drink users. Parents should regard frequent energy drink consumption as a red flag for heavy drinking in their college-aged children, and discourage mixing alcohol and energy drinks. Young adults should be educated about the risks of this behavior and encouraged to exercise vigilance and intervene appropriately when they observe their peers consuming energy drinks in risky situations. For example, they should be educated to understand the difference between someone who is impaired but wide awake and someone who is safe to drive. This could be a natural extension of highly successful past campaigns that have made the concept of a “designated driver” second nature for many young adults.
Further study is certainly warranted to understand how patterns of co-ingestion of alcohol and energy drinks relate to the risk for serious alcohol problems. Strong evidence now exists supporting the notion that mixing energy drinks with alcohol leads to greater alcohol consumption and therefore more dangerous blood alcohol levels (Thombs et al., 2010
). Moreover, in light of the commonalities between the characteristics of energy drink users and heavy drinkers, future studies should strive to account for multiple risk factors and any multicollinearity between them.