Alcohol increases social engagement in dyadic interactions: role of partner's drug state.

Rationale: Alcohol is commonly used in social environments and is known to facilitate social behaviors. However, most controlled laboratory studies on alcohol have been conducted in isolated settings, limiting our understanding of its effects on social interactions.

Objectives: The current study was designed to examine the effects of alcohol on dyadic interactions in healthy volunteers (N = 37), with a focus on the influence of the conversation partner's drug state.

Methods: Using a 4-session, placebo-controlled, within-subjects design, participants received a moderate dose of alcohol (0.8 g/kg men) or placebo in randomized order before engaging in a 45-minute semi-structured conversation with a partner who received either alcohol or placebo. Partners were always strangers. Outcome measures included subjective responses to alcohol, self-reported closeness to partners, and facial expressions during interactions analyzed via a machine learning model.

Results: Alcohol produced its expected subjective effects, some of which were enhanced when the partner also received alcohol. Alcohol enhanced enjoyment of social interactions and feelings of connectedness, irrespective of the partner's drug condition. Facial expression analysis revealed that alcohol increased positive and decreased negative emotional expressions. For women but not men, these effects were more pronounced when their conversation partners also received alcohol. Individual emotion analysis revealed that alcohol increased the intensity of facial expressions associated with amusement, joy, and excitement, while reducing emotions such as awkwardness and contempt.

Conclusions: Our findings show that alcohol increases feelings of social connectedness, and that responses to alcohol can be influenced by the drug state of interacting partners. The increased feelings of social connection may contribute to risk for escalation of use.