Exploring trial acceptability, recruitment, and retention in a pilot optimisation randomised controlled trial of a behavioural intervention to support medication adherence in women with breast cancer: A qualitative process evaluation.

Background: Complex factorial trials are increasingly employed to optimise complex behavioural interventions. However, acceptability of such designs to participants are unknown. In this qualitative process evaluation of a pilot optimisation randomised controlled trial (O-RCT) for a behavioural intervention to support medication adherence in women with breast cancer, we explored acceptability of trial participation, alongside barriers and facilitators to recruitment and retention. Methods: We conducted a 2 Results: Generally, participation in the trial was perceived positively ( Conclusions: This qualitative process evaluation suggests participation in an O-RCT was acceptable. Low randomisation coherence and questionnaire burden are notable areas for improvement. Future studies within trials should explore approaches to explaining factorial trials to participants. Barriers and facilitators to recruitment and retention were similar to parallel group randomised trials, suggesting interventions addressing these may be applicable regardless of trial design.