The effects of caffeine and glucose on cognitive performance and
subjective mood were tested in a double-blind, balanced, placebocontrolled
within-subjects design. For this, participants received two
drinks labeled “coffee” and “energy drink” at the same time. Two versions,
one containing an active ingredient (caffeine or glucose) and
one without the active ingredient (placebo), were prepared for each
drink. Participants were naïve as to the different compositions and unable
to discriminate the active and placebo conditions, as we had
asked them after completion of the study whether they had noticed
any differences in taste or flavor between the respective drinks, which
was never the case. These findings are in line with a pilot study (N =
5). The composition of the two drinks differed across treatment conditions
as follows: (1) the CAFFEINE treatment consisted of a decaffeinated
coffee with added caffeine and an artificially sweetened placebo
drink; (2) for the GLUCOSE treatment, a decaffeinated placebo coffee
and a glucose drink were administered; (3) in the PLACEBO condition,
subjects received a decaffeinated coffee and an artificially sweetened
drink. All beverages were based on distilled water. The PLACEBO coffee
was prepared using 2 g of decaffeinated instant coffee powder