Social networks can be a vital mechanism for users to adapt to changes induced by new IT systems in organizations. However, we do not adequately understand the effect of social networks on post-adoption IT use. Drawing on coping theory and the social network literature, we develop a cognitive-affective-behavioral classification of user adaptation and identify seeking-network closure and giving-network closure as key network characteristics pertinent to post-adoption IT use. Thereafter, we establish a theoretical link from seeking-network closure and giving-network closure to post-adoption IT use through the underlying mechanisms of user adaptation. We operationalize the research model using a field survey of a newly implemented electronic medical record system in a hospital in Northeast China, where we collected network data and objective system logs of 104 doctors. We found that seeking-network closure was positively associated with cognitive adaptation but negatively associated with affective adaptation and behavioral adaptation, whereas giving-network closure was negatively associated with cognitive adaptation but positively associated with affective adaptation and behavioral adaptation. Moreover, cognitive adaptation and affective adaptation were determinants of post-adoption IT use, but behavioral adaptation was not. We discuss our study’s theoretical and practical contributions. © 2017, Association for Information Systems. All rights reserved.