Clubgoers and Their Trendy Cocktails: Implications of Mixing
Caffeine Into Alcohol on Information Processing and Subjective
Reports of Intoxication
Cecile A. Marczinski and Mark T. Fillmore
University of Kentucky
Alcoholic drink preferences in college students have made an interesting shift recently, with
trends in consumption leaning toward caffeinated alcohol in various forms (e.g., Red Bull and
vodka or caffeinated beers such as Anheuser-Busch’s B-to-the-E). Despite the dramatic rise
in popularity of these beverages, little research has examined the combined effects of alcohol
and caffeine, which is problematic for adequately informing the public about the risk or lack
thereof of these drinks. The purpose of this study was to directly investigate the acute effects
of alcohol and caffeine, alone and in combination, on well-validated measures of cognitive
performance and subjective intoxication in social drinkers. Participants (N ? 12) performed
a psychological refractory period task that measured dual-task interference as the prolonged
reaction time to complete the 2nd of 2 tasks performed in close temporal sequence. Perfor-
mance was tested under 2 active doses and 1 placebo dose of caffeine (0.0 mg/kg, 2.0 mg/kg,
and 4.0 mg/kg) in combination with 1 active dose and 1 placebo dose of alcohol (0.0 g/kg
and 0.65 g/kg). As expected, alcohol impaired task performance by increasing dual-task
interference and increasing errors. The coadministration of caffeine counteracted the effects
of alcohol on interference but had no effect on the degree to which alcohol increased errors.
Subjective measures of intoxication showed that coadministration of caffeine with alcohol
reduced participants’ perceptions of alcohol intoxication compared with administration of
alcohol alone. The results highlight the complexity of drug interactions between alcohol and
Keywords: alcohol, caffeine, information processing, intoxication, college students
Alcoholic drink preferences in college students have
made an interesting shift in the last decade, with clubgoers
increasingly drawn to caffeinated alcoholic drinks in vari-
ous forms. With the national introduction of Red Bull to the
United States in 2001, young partygoers became enamored
with using the beverage as a mixer for their alcoholic drinks,
presumably for the purpose of reducing the depressant ef-
fects of alcohol and thus allowing them to party longer. This
increased popularity of caffeinated alcoholic beverages
among college students was quickly identified by the bev-
erage industry in North America. In 2005, several “energy”
beers and malt beverages were introduced, including An-
heuser-Busch’s B-to-the-E (54 mg caffeine in 6.6% alcohol
by volume), New Century Brewing’s Moon Shot (45 mg
caffeine in 4.8% alcohol by volume), Labatt’s Shok (60 mg
caffeine in 6.9% alcohol by volume), and Molson’s Kick
(55 mg caffeine in 5% alcohol by volume).
Some physicians have warned of the potential health
implications of mixing caffeine and alcohol, such as in-
creased risk of dehydration (American Medical Association,
2003). Although the various energy drinks and beers also
contain other stimulant compounds, such as taurine, theoph-
ylline, theobromine, and ginseng, the health concerns of
these drinks have been in relation to the high caffeine
content. Caffeine is the common stimulatory compound in
all of these beverages. Of interest, the U.S. Food and Drug
Administration (FDA) does not regulate the caffeine content
of energy drinks, and recent analyses have determined that
the caffeine content of these drinks can contain 150%–
300% of the amount of caffeine that the FDA allows for
cola beverages (McCusker, Goldberger, & Cone, 2006).
However, there have been surprisingly few investigations
into the presumption that these caffeinated alcohol drinks
allow drinkers to consume greater amounts of alcohol be-
cause the sedation and behaviorally impairing effects nor-
mally associated with the drug are offset by the coconsump-
tion of caffeine (Ferreira, de Mello, Pompeia, & de Souza-
Formigoni, 2006). Although to date there has been no
published study of North American drinkers’ motivations
Cecile A. Marczinski and Mark T. Fillmore, Department of
Psychology, University of Kentucky.
This research was supported by a grant from the Alcoholic
Beverage Medical Research Foundation, awarded to Cecile A.
Marczinski; National Institutes of Health National Research Ser-
vice Award DA07304 from the National Institute on Drug Abuse,
awarded to Cecile A. Marczinski; and National Institute on Alco-
hol Abuse and Alcoholism Grant R01 AA12895, awarded to Mark
Correspondence concerning this article should be addressed to
Mark T. Fillmore, Department of Psychology, University of Ken-
tucky, Lexington, KY 40506-0044. E-mail: firstname.lastname@example.org
Experimental and Clinical Psychopharmacology
2006, Vol. 14, No. 4, 450–458
Copyright 2006 by the American Psychological Association
for using caffeinated alcoholic drinks, a small survey of
college students in Brazil (N ? 136) examined their moti-
vations for using these drinks (Ferreira, de Mello, & For-
migoni, 2004). The authors reported that 76% of the sample
indicated regular use of energy drinks in combination with
alcohol (mainly whiskey, vodka, or beer). Of those who
reported use of caffeinated alcohol, 38% reported that the
combination drinks increased happiness, 30% reported eu-
phoria from these drinks, 27% reported uninhibited behav-
ior from these drinks, and 24% reported increased physical
vigor. Other reports from Ireland and Germany have impli-
cated these drinks in assaults and automobile accidents,
respectively, suggesting that the combination of caffeine
and alcohol impairs the ability to correctly assess level of
intoxication and the ability to drive more greatly than alco-
hol intoxication alone (Riesselmann, Rosenbaum, &
Schneider, 1996; Tormey & Bruzzi, 2001). Correspond-
ingly, Denmark, France, and Norway have placed bans on
the sale of Red Bull, citing health concerns.
Caffeine acts as an adenosine receptor antagonist, with
the central nervous system (CNS) stimulatory effects of
caffeine largely due to blockage of adenosine A2A recep-
tors that stimulate GABAergic neurons of inhibitory path-
ways to the dopaminergic reward system of the striatum
(Cauli & Morelli, 2005; Mandel, 2002; Nehlig, Daval, &
Debry, 1992). In addition, caffeine also acts as a CNS
stimulant as it is an indirect agonist of noradrenaline (Lader
& Bruce, 1989). Laboratory studies of the behavioral effects
of caffeine show that the drug can generally enhance skilled
performance by allaying fatigue, increasing vigilance,
speeding reaction time (RT), and prolonging effort (for
reviews, see Nehlig et al., 1992; Weiss & Laties, 1962). The
extent to which the coadministration of caffeine can coun-
teract or functionally antagonize alcohol-induced behavioral
impairment also has been studied in the laboratory; how-
ever, the findings have been mixed. Some studies have
shown that caffeine coadministration can reduce the impair-
ing effects of alcohol on some global performance tasks
(Burns & Moskowitz, 1990; Fillmore & Vogel-Sprott,
1999; Franks, Hagedorn, Hensley, Hensley, & Starmer,
1975; Kerr, Sherwood, & Hindmarch, 1991; Martin & Gar-
field, 2006; Rush, Higgins, Hughes, Bickel, & Wiegner,
1993). However, other studies have failed to demonstrate
consistent counteracting effects of caffeine (Fillmore &
Vogel-Sprott, 1995; Liguori & Robinson, 2001). Research
reviews also have noted these discrepancies with regard to
alcohol–caffeine interactions, leading to conclusions that
evidence for caffeine antagonism is equivocal (e.g., Fudin &
Reasons for these inconsistencies are not clear. However,
the tasks used in these studies varied widely in their com-
plexity and in the specific behavioral and cognitive mech-
anisms involved in their performance (e.g., memory, motor
coordination, RT). We recently argued that the equivocal
evidence for caffeine antagonism of alcohol-induced im-
pairment might reflect the fact that not all cognitive and
behavioral impairments from alcohol can be offset by the
coadministration of caffeine. For example, in a study of the
separate and combined effects of moderate doses of alcohol
(0.65 g/kg) and caffeine (2.0 and 4.0 mg/kg), we showed
caffeine could counteract alcohol-induced slowing of re-
sponse time but not the disinhibiting effects of the drug
(Marczinski & Fillmore, 2003). Thus, it appears that the
ability of caffeine to counteract alcohol-induced impairment
could depend greatly on the specific nature of the cognitive
and behavioral processes involved.
Another important consideration concerns the degree of
behavioral demands imposed by the particular activity being
performed. It is well known from studies of divided atten-
tion that alcohol impairment can be intensified in situations
of high behavioral demand (Holloway, 1995; Linnoila,
1974). A divided attention task essentially requires an indi-
vidual to perform two tasks simultaneously—for example,
manually tracking a moving object (e.g., a pursuit task)
while performing an auditory discrimination task (e.g., de-
tecting differences among tones). Related are dual-task sit-
uations. Typically, dual-task performance is measured by
requiring an individual to respond to each of two stimuli
(Tasks 1 and 2) presented in very close temporal proximity
(for a review, see Pashler, 1994). These situations often
illustrate the limits of human information processing. Char-
acteristically, an interference effect is observed as a slowing
of response time to the second stimulus (Task 2). The
delayed response time to the second stimulus is attributed to
the psychological refractory period (PRP) and is assumed to
reflect a limitation of information processing in which the
response to Task 2 must be delayed until processing of
Task 1 is complete (Johnston & Heinz, 1978). Performance
in dual-task situations is highly sensitive to the disruptive
effects of alcohol. Studies of alcohol effects in dual-task
situations show that moderate doses of alcohol dramatically
increase task impairment, even in simple tasks that show no
impairment from alcohol when performed in isolation (Fill-
more & Van Selst, 2002; Schweizer, Jolicoeur, Vogel-
Sprott, & Dixon, 2004).
Outside the laboratory, the disruptive effects of alcohol
often occur in complex, behaviorally demanding environ-
ments that require the simultaneous performance of multiple
activities (i.e., the operation of a motor vehicle). Laboratory
assessment of dual-task performance may hold greater eco-
logical validity as models of day-to-day performance of
activities outside the laboratory. As yet, no research has
applied the dual-task PRP model to the investigation of
alcohol–caffeine interactions. In the present study, we ex-
amined healthy adults and tested the separate and combined
effects of alcohol and caffeine on their ability to process
information in a dual-task situation. Performance was tested
under two active doses and one placebo dose of caffeine
(0.0 mg/kg, 2.0 mg/kg, and 4.0 mg/kg) in combination with
one active dose and one placebo dose of alcohol (0.0 g/kg
and 0.65 g/kg). The active alcohol dose (0.65 g/kg) used in
the study has been shown to impair information processing
in the dual-task situation (Fillmore & Van Selst, 2002). The
active caffeine doses (2.0 mg/kg and 4.0 mg/kg) were
selected to approximate the caffeine content found in the
various caffeinated beers and mixed alcoholic energy drinks
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Received April 19, 2006
Revision received August 7, 2006
Accepted August 7, 2006 ?
MARCZINSKI AND FILLMORE