The timeline followback reliably assesses caffeinated alcohol beverage consumption and outcomes: caffeinated alcoholic beverages increase risk

Background: Daily diary studies have shown that caffeinated alcoholic beverages (CABs) are associated with more risk than consuming alcohol alone; however, daily diary studies are time intensive. The Timeline Followback (TLFB) is a practical alternative, but its ability to reliably collect CAB information is unknown.

Methods: In the current study, 189 university students completed a modified TLFB interview twice, 2 weeks apart. The interview assessed alcohol and caffeine quantities, along with the type of caffeine consumed so that drinking occasions could be classified into four different types: alcohol-only, alcohol mixed with energy drinks (AmEDs), alcohol mixed with caffeine other than energy drinks, and AmEDs plus other sources of caffeine. The interview also obtained outcomes for each type of drinking occasion (duration of drinking, perceived intoxication level, and the number of problems encountered).

Results: Two-week test–retest reliability was excellent for 21 of 24 mTLFB variables. The remaining three indices demonstrated good test–retest reliability. These indices involved AmEDs. TLFB event-level data revealed that occasions that involved CABs occurred less frequently and involved greater quantities of alcohol, longer drinking durations, greater perceived intoxication, more alcohol-related consequences than occasions involving only alcohol. Drinking occasions involving AmEDs incurred the most risk and these occasions were associated with greater caffeine quantities than non-ED CAB occasions.

Conclusions: The mTLFB can be used to obtain a reliable assessment of event-level behavior for CABs. As perceived intoxication was higher for CAB occasions than alcohol-only occasions, future studies should examine the validity of the masking hypothesis, which asserts that caffeine causes people to underestimate their blood alcohol content.