Context: The use of the Internet for peer-to-peer connection has been one of its most dramatic and transformational features. Yet this is a new field with no agreement on a theoretical and methodological basis. The scientific base underpinning this activity needs strengthening, especially given the explosion of web resources that feature experiences posted by patients themselves. This review informs a National Institute for Health Research (NIHR) (UK) research program on the impact of online patients' accounts of their experiences with health and health care, which includes the development and validation of a new e-health impact questionnaire. Methods: We drew on realist review methods to conduct a conceptual review of literature in the social and health sciences. We developed a matrix to summarize the results, which we then distilled from a wide and diverse reading of the literature. We continued reading until we reached data saturation and then further refined the results after testing them with expert colleagues and a public user panel. Findings: We identified seven domains through which online patients' experiences could affect health. Each has the potential for positive and negative impacts. Five of the identified domains (finding information, feeling supported, maintaining relationships with others, affecting behavior, and experiencing health services) are relatively well rehearsed, while two (learning to tell the story and visualizing disease) are less acknowledged but important features of online resources. Conclusions: The value of first-person accounts, the appeal and memorability of stories, and the need to make contact with peers all strongly suggest that reading and hearing others' accounts of their own experiences of health and illnesss will remain a key feature of e-health. The act of participating in the creation of health information (e.g., through blogging and contributing to social networking on health topics) also influences patients' experiences and has implications for our understanding of their role in their own health care management and information. © 2012 Milbank Memorial Fund.
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