Cognitive Effects of Energy Drinks
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Party Like a Rockstar:
The Effect of Energy Drinks on Cognitive Ability
Lead Author Adam Serfling
Co-Researchers Brittney Hetzel & Leanne Ykema
Winona State University
Abstract
Energy drinks have increased in popularity in recent history due to their claims of
increased physical energy and cognitive abilities. Rockstar Juiced Energy Drink was
tested to see whether manufacturer claims of increased cognitive abilities were true.
Cognitive abilities were tested by having participants completed Stroop Effect Tests.
Participants would identify the ink-color on two lists of words, one list containing
words in common usage and the other containing color-names which were printed in
an incongruent color. Participants then consumed eight ounces of Rockstar Juiced
Energy Drink and repeated the Stroop Effect Tests after 15 minutes. The results
indicated that Rockstar Juiced Energy Drink did not reduce the interference and
therefore did not improve cognitive abilities. Rockstar Juiced Energy Drink did
significantly improve participant reaction times which allowed them to complete the
Stroop Tests faster than those who did not consume the energy drink.
Party Like a Rockstar:
The Effects of Energy Drinks on Cognitive Ability
Energy drinks have recently come to the forefront of pop culture. Often considered to be a trendy
mixer for night clubs or a quick eye-opener for an early morning, energy drinks are everywhere. Due
to the massive amounts of caffeine and other trendy herbs such as taurine and guarana, manufacturers
have been marketing energy drinks as a beverage that not only increases energy but also cognitive
ability. Numerous studies have been conducted on the true effects of energy drinks; however, few have
been shown to conclusively adhere to manufacturers’ claims.
Research conducted by Seidl, Peyrl, Nicham, & Hauser, (2000) focused on the improvement of
mood and reaction times. A double-blind, placebo-controlled study measured reactions times and also
mood. Graduate students ingested capsules containing caffeine, taurine, and glucuronolactone which is
the main ingredients in numerous energy drinks or a placebo capsule. Starting at dusk, participants
conducted reaction time exercises and also completed mood questionnaires every hour until midnight.
At the end of the experiment, motor reaction times were significantly longer compared with baseline
measurements in the placebo group, but were unchanged in the energy drink ingredients group. In the
mood evaluation, scores for feelings of well-being, vitality scores, social extroversion, and total scores
decreased in the placebo group, but remained the same for those in the energy drink ingredients group
(Seidl, et.al, 2000). This suggests that the ingredients in energy drinks have a positive effects upon
mental performance and mood.
Cognitive Effects of Energy Drinks
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Other research has often deprived participants of caffeine for 10 hours or more before the study.
Much of the positive results shown from these types of experiments have thought to be due to the
reversal of caffeine withdrawal. Another study looked for improvement due to energy drinks for
participants who were not caffeine deprived. Participants in one study were allowed ad libitum
caffeinated beverages until one hour before testing while the other study had no restrictions on caffeine
use. Participants were then given an energy drink or one of two placebos: a sugar-free drink or a sugar
containing drink to assess the effects of sugar. Participants were then tested with a rapid visual
information test, a verbal reasoning test, a verbal and non-verbal memory test and a set of mood
measures. In both studies, the energy drink produced improved attention and verbal reasoning in
comparison to the sugar-free and sugar-containing beverages. There were no effects on memory found,
nor were any differences in performance between the sugar-free and sugar-containing beverages
(Warburton, Bersellini, and Sweeney, 2001). This suggests that the ingredients in energy drinks do
improve attention and reaction time. In the following experiment, it is predicted that energy drinks will
overcome the interference caused by the Stroop Effect, hereby improving reaction times for such
experiments.
Methods
Participants
Thirty-eight students (7 males, 31 females) from a small, Midwest university were recruited using
sign-up sheets in the Psychology department. Participants were given one point of extra-credit by their
respective Psychology professors for participating in the experiment.
Materials
Two Stroop test sheets were constructed on 8 ½” x 11” white paper. The color condition contained
18 words consisting of nine names of colors (green, blue, red, yellow, purple, orange, pink, black, and
white) printed in 27 pt Verdana font so they could be filled with color using markers. The color names
were randomly arranged so that each was used only twice. The words were filled in using eight colors
(red, yellow, purple, orange, pink, brown, green, and blue) and in a fashion so that the color of the ink
was incongruent with the color name printed on the paper. One color name (orange) was mistakenly
colored so that the name and color matched during the sheet construction. Being that black is the
common print color and white is rarely used in print, brown was used as a fill in color for black and
white was not used at all. This resulted in two colors (red and orange) being used as a fill in color three
times each. The word condition contained 18 words consisting of 9 words in common usage not
associated with a color (troop, show, cat, rabbit, candle, image, lint, clock, and house). These words
were chosen and arranged so that they matched the color condition in both number of letters and
vowel/consonant make-up. The words were printed in the same font and size as in the color condition
and were colored so that the order of colors used matched that of the color condition. Rockstar Juiced,
a popular orange juice energy drink was also used in red, 16 ounce plastic cups for those in the
Rockstar energy drink condition. An episode of the popular television show “Scrubs” was used to pass
the time between testings.
Procedure
Participants were randomly assigned to either the Rockstar energy drink condition or the no
Rockstar condition by test group. Each test group consisted of up to three participants dependent on
the number of researchers present. This ensured that each participant would be tested at the same time,
with the equal time intervals between tests. Each test group was told that they would be asked to
complete a short exercise. Participants were instructed to, as quickly as they could, go through the list
of words and identify the color each word is printed in. Participants were told that if they made a
mistake, they would be notified by the researcher, and they must correct their mistake before moving
on to the next word. Participants were told that the time would start after the administrator flipped over
the test sheet and said “Ready? Begin.” Time would be stopped upon the correct completion of each
test sheet. Participants were randomly assigned to complete the exercise in the order of color, word,
Cognitive Effects of Energy Drinks
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word, color or word, color, color, word in order to counterbalance for the order effect. Participants
were then separated and conducted the exercise alone with an administrator.
Upon completion of this exercise, participants were brought back together. Groups that were
randomly assigned to the Rockstar condition then were given an eight ounce glass of Rockstar Juiced
Energy Drink. Participants were instructed to drink this beverage as quickly as they could, but not so
quickly that they became ill. Most participants had no problems consuming this drink in less than one
minute. The No Rockstar condition was not given any beverage. Both conditions then were told they
would watch part of an episode of Scrubs, a popular television sitcom. Fifteen minutes later, the
administrators stopped the sitcom and separated the participants again. Participants then completed the
first exercise again in the same way. Upon completing the exercise for the second time, participants
were regrouped, thanked and debriefed.
Results
A 2x2 ANOVA was conducted to test the effects of Rockstar Juiced Energy Drink on cognitive
ability. Cognitive ability was measured using Stroop Effect Tests using a color incongruence and
standard word tests. Improvement scores were found by subtracting the post-test measure from the pretest measure. Higher mean scores indicate a greater level of improvement. Means can be seen in Table
1. There was not a significant interaction between Rockstar consumption and the Stroop Effect, F
(1,36) = .001, p = .979. This suggests that Rockstar does not overcome the interference created by the
Stroop Effect. There was a significant main effect for the Stroop Effect; Stroop interference caused
times on the color condition to be longer than on the word condition, F (1,36) =6.07, p = .019. There
was also a significant main effect for Rockstar Juiced Energy Drink; Rockstar caused an improvement
in times in both the color and word conditions, F (1,36) = 4.18, p = .048. This suggests that Rockstar
Juiced Energy Drink causes greater improvements on Stroop Effect Tests, but does not reduce the
interference caused by the color condition.
Figure 1. Mean time improvements in seconds for color and word Stroop conditions with and without
Rockstar Juiced Energy Drink.
Mean Improvement (Seconds)
3
2.5
2
1.5
Rockstar
No Rockstar
1
0.5
0
Color Condition
Word Condition
Stroop Condition
Cognitive Effects of Energy Drinks
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Table 1 Mean (SD) improvement in Stroop Effect Tests when given an energy drink or no
energy drink.
Stroop
Color Words
Other Nouns
Energy Drink
Rockstar
No Rockstar
Total
Rockstar
No Rockstar
Total
Mean (SD)
2.41 (2.04)
1.60 (1.66)
2.03 (1.89)
1.59 (1.42)
0.76 (1.13)
1.19 (1.34)
Discussion
Energy drinks have always marketed themselves as being a drink that both increases physical
energy and also improves mental functioning. In this study, Rockstar Energy Drink was projected to
decrease the amount of interference caused by the Stroop Effect. The Stroop Effect Test was used to
measure cognitive ability due to its standing as an established psychological phenomenon. The color
incongruence Stroop Test was used as it is the most demonstrative of the effects of interference.
Contrary to projections, Rockstar Juiced Energy Drink did not reduce or have a noticeable effect
on interference created by the Stroop Effect Tests. However, Rockstar Juiced Energy Drink did
significantly make the participants complete the Stroop Effect Test faster than those that did not
receive the energy drink. This is likely due to a reduction of fatigue from the caffeine in the energy
drink. This is in line with the common usage of caffeinated beverages to increase available energy and
also reduce drowsiness. These results suggest that although the energy drink did not increase cognitive
ability on participants, it did reduce reaction times. In other words, Rockstar Juiced Energy Drink
made participants faster, but not smarter on Stroop Effect Tests.
The Stroop Effect Test may have not been the best measure of cognitive ability. Stroop Tests are
generally quite short and scores are improved quite quickly due to practice effects. Participants seemed
to quickly pick up on tricks to improve times as some participants began memorizing the first few
colors of each sheet. Future research should broaden and focus on tasks indicative of cognitive ability
such as testing, free recall, or word association tasks.
References
Seidl, R., Peyrl, A., Nicham, R., & Hauser, E. (2000). A taurin and caffeine-containing drink stimulates
cognitive performance and well-being. Amino Acids, 19, 635-642.
Warburton, D.M., Bersellini, E., & Sweeney, E. (2001). An evaluation of a caffeinated taurin drink on
mood, memory and information processing in healthy volunteers without caffeine abstinence.
Psychopharmacology, 158, 322-328.