Participants
Twenty healthy participants (14 males) with the mean (±SD) age of 22.2 (± 4.1) were recruited. They had a mean weight (± SD) of 80.3 kg (± 20.0) and 14.6 (±1.5) years of education. All except three were a regular consumer of caffeine (have taken at least one cup of caffeine-containing drinks per day, with 1.6 (±1.1) mean (±SD) cup of coffee or tea). Three of them consumed cannabis in the last two months, four of them smoke cigarette and two of them consumed amphetamine in the last month.