Lay-expert communities have exposed the vulnerabilities of professional expertise to promote alternative advice that offer better solutions to their problems. Despite the importance of these communities in challenging professional expertise and promoting social change and innovation, an important but unanswered question is how lay experts contest the authority of professional expertise, persuading others to adopt their alternative advice. Our study reveals the processes through which patients in a diabetes online community legitimised alternative treatment regimens and delegitimised treatments prescribed by medical professionals. We unveil two processes – imitating professional experts and differentiating from professional experts – through which lay-expert communities succeed in delegitimising professional expertise to convince others of the legitimacy of their alternative advice. These processes are characterised by ambivalence and contradictions between the rituals and standards of professionals that lay experts emulate to gain legitimacy for their own expertise, and the standards and values they create to contest the authority of professional experts and maximise adoption of their alternative advice. By unveiling these processes, our contribution is to show how legitimation of alternative advice by lay-expert communities is much more complex and contested than current research on lay expertise suggests and presents far more tensions than the professionals’ route of legitimation.
