How AI and Human Behaviors Shape Psychosocial Effects of Chatbot Use: A Longitudinal Randomized Controlled Study

AI chatbots, especially those with voice capabilities, have become increasingly human-like, with more users seeking emotional support and companionship from them. Concerns are rising about how such interactions might impact users' loneliness and socialization with real people. We conducted a four-week randomized, controlled, IRB-approved experiment (n=981, >300K messages) to investigate how AI chatbot interaction modes (text, neutral voice, and engaging voice) and conversation types (open-ended, non-personal, and personal) influence psychosocial outcomes such as loneliness, social interaction with real people, emotional dependence on AI and problematic AI usage. Results showed that while voice-based chatbots initially appeared beneficial in mitigating loneliness and dependence compared with text-based chatbots, these advantages diminished at high usage levels, especially with a neutral-voice chatbot. Conversation type also shaped outcomes: personal topics slightly increased loneliness but tended to lower emotional dependence compared with open-ended conversations, whereas non-personal topics were associated with greater dependence among heavy users. Overall, higher daily usage - across all modalities and conversation types - correlated with higher loneliness, dependence, and problematic use, and lower socialization. Exploratory analyses revealed that those with stronger emotional attachment tendencies and higher trust in the AI chatbot tended to experience greater loneliness and emotional dependence, respectively. These findings underscore the complex interplay between chatbot design choices (e.g., voice expressiveness) and user behaviors (e.g., conversation content, usage frequency). We highlight the need for further research on whether chatbots' ability to manage emotional content without fostering dependence or replacing human relationships benefits overall well-being.