‘Medically unexplained symptoms’ (MUS), through the lens of the biopsychosocial model, are understood in mainstream psy disciplines and related literature as a primarily psychosocial phenomenon perpetuated by ‘dysfunctional’ psychology on the part of people labelled with such. Biopsychosocial discourse and practice in this field, underpinned by little empirical foundation and lacking theoretical coherency, are associated with harms sustained by people labelled with MUS. Yet, little attention is paid to the psychology of social actors and institutions whose practice and policy derives from biopsychosocial theorising, or whose vested interests (re)produce such theorising. This article contends that lack of reflexivity among psy practitioners and other social actors on individual, institutional and structural levels furthers biopsychosocial hegemony and contributes to harms. Non-reflexive behaviour on the part of practitioners within clinical and ‘therapeutic’ encounters and on the part of social actors within institutions and broader power structures is examined, and possible psychological underpinnings of non-reflexivity are explored. Notably, the concept of gain, drawn from dominant discourse around MUS, is applied broadly to explore what might be gained from eschewing reflexivity and from adhering to biopsychosocial narratives. Implications for practice, supervision, training and research are discussed, notably highlighting a need for critical reflexivity in all domains.