Some previous studies have demonstrated an early effect of caffeine administration on subjective state, but none of them has explored its existence after the administration of decaffeinate coffee, nor the possible differences according to the gender. The aim of the present work was to investigate, using a realistic design (non-research settings and naturalistic administration of the drug), the early effects (10-30 min post-consumption) of a single low-moderate dose of caffeine (100 mg) and decaffeinate coffee on sleepiness and subjective activation.

A random double-blind informed placebo controlled procedure was applied to a group of 688 healthy undergraduate volunteers (238 men) mean age 22.03 ± 2.21 years. Measures were recorded in two experimental sessions: morning 11:00-13:00h or afternoon 16:00-18:00h, in three moments before (30, 20 and 10 min.) averaged as a stable baseline, and three after (10, 20 and 30 min.) consumption.

Caffeine administration induces fewer somnolence (F= 159.776, p<0.0001) and greater activation (F= 43.516, p<0.0001) in all post-consumption records, while the decaffeinated drink only induced arousing effects in the 10 min. post-consumption record. Caffeine effects were greater in men and the decaffeinated beverage produced greater effect in women (sleepiness: F= 14.893, p<0.0001; activation: F= 4.229, p=0.038).

Future works should study more accurately the early effect of caffeine and decaffeinate coffee and the influence of gender, using other parameters which have proven to be sensitive to their administration, as well as several caffeine doses.