Caffeine preference during 24 h continuous and intermittent access to caffeine. (A) Percent caffeine preference across continuous (green) and intermittent (purple) drinking days. Caffeine preference significantly decreased compared with the initial 2-day average during continuous access on days 16–28, shortly after the beginning of intermittent access. The data are expressed as 2-day averages for each data point. *p < 0.05, compared with day 2. (B) Percent caffeine preference in the high preference group (dark pink), medium preference group (pink), and low preference group (light pink) across continuous (green) and intermittent (purple) drinking days. The data are expressed as 2-day averages for each data point. (C) Average caffeine preference in the high, medium, and low preference groups across the entire continuous and intermittent periods. The medium and low preference groups exhibited significantly lower preference for caffeine (*p < 0.05). The medium preference group exhibited significantly higher preference for caffeine than the low preference group (#p < 0.05).