BACKGROUND Qualitative studies of participants' experiences in randomised clinical trials (RCTs) suggest that the psychosocial context of treatment in RCTs may be quite different to the psychosocial context of treatment in usual practice. This is important, as the psychosocial context of treatment is known to influence patient outcomes in chronic illness. Few studies have directly compared the psychosocial context of treatment across RCTs and usual practice. In this study, we explored differences in psychosocial context between RCT and usual practice settings, using acupuncture as our model. METHODS We undertook a secondary analysis of existing qualitative interviews with 54 patients. 27 were drawn from a study of western and traditional acupuncture in usual practice (for a range of painful conditions). 27 were drawn from a qualitative study nested in an RCT of western acupuncture for osteoarthritis of the hip or knee. We used qualitative analysis software to facilitate an inductive thematic analysis in which we identified three main themes. RESULTS In usual practice, starting acupuncture was more likely to be embedded in an active and ongoing search for pain relief, whereas in the RCT starting acupuncture was opportunistic. Usual practice patients reported few uncertainties and these had minimal consequences for them. In the RCT, patients experienced considerable uncertainties about their treatment and its effectiveness, and were particularly concerned about whether they were receiving real (or fake) acupuncture. Patients stopped acupuncture only at the end of the fixed course of treatment in the RCT, which was similar to those receiving acupuncture in the public sector National Health Service (NHS). In comparison, private sector patients re-evaluated and re-negotiated treatments particularly when starting to use acupuncture. CONCLUSIONS Differences in psychosocial context between RCTs and usual practice could reduce the impact of acupuncture in RCT settings and/or lead to under-reporting of benefit by patients in trials. New trial designs that ensure participants' experiences are similar to usual practice should minimise differences in psychosocial context and help attenuate these potentially confounding effects.