MOR KO (A) and Dlx-MOR KO (B) mice consume less alcohol than their corresponding controls in an alcohol continuous-access 2-bottle-choice drinking paradigm. Animals were offered access to alcohol (10% v/v) (A-B) and water (C-D) in their home cages for 14 consecutive days (14 sessions). Values are presented as the daily mean g/kg of alcohol intake (±SEM) and ml/kg of water intake (±SEM), respectively. Alcohol preference (E-F) was calculated by dividing the total alcohol solution consumed by total fluid (alcohol plus water) consumption. Left panels represent the mean (±SEM) of alcohol and water consumption or alcohol preference per session; Right Panels represent mean (±SEM) of daily alcohol and water consumption or alcohol preference during the entire experiment. (A, C, E) n = 9-10, (B, D, F) n=9-12 for each group. *p < 0.05.