Rationale
Combining alcohol and caffeine is associated with increased alcohol
consumption, but no prospective experimental studies have examined whether added
caffeine increases alcohol consumption.
Objectives
This study examined how caffeine alters alcohol self-administration and
subjective reinforcing effects in healthy adults.
Methods
Thirty-one participants completed six double-blind alcohol self-administration
sessions: three sessions with alcohol only (e.g., Beverage A) and three sessions with
alcohol and caffeine (e.g., Beverage B). Participants chose which beverage to consume on
a subsequent session (e.g., Beverage A or B). Effects of caffeine on overall beverage
choice, number of self-administered drinks, subjective ratings (e.g., Biphasic Alcohol
Effects Scale), and psychomotor performance were examined.
Results
A majority of participants (65%) chose to drink the alcohol beverage
containing caffeine on their final self-administration session. Caffeine did not
increase the number of self-administered drinks. Caffeine significantly increased
stimulant effects, decreased sedative effects, and attenuated decreases in psychomotor
performance attributable to alcohol. Relative to nonchoosers, caffeine choosers reported
overall lower stimulant ratings, and reported greater drinking behavior prior to the
study.
Conclusions
Although caffeine did not increase the number of self-administered drinks, most
participants chose the alcohol beverage containing caffeine. Given the differences in
subjective ratings and pre-existing differences in self-reported alcohol consumption for
caffeine choosers and nonchoosers, these data suggest decreased stimulant effects of
alcohol and heavier self-reported drinking may predict subsequent choice of combined
caffeine and alcohol beverages. These predictors may identify individuals who would
benefit from efforts to reduce risk behaviors associated with combining alcohol and
caffeine.