Comparing process evaluations of motivational interviewing interventions for managing health conditions and health promotions: A scoping review

•Process evaluation can help us understand how MI works.•Process evaluation can inform how MI should be implemented.•MI is often implemented with insufficient fidelity and dose to be effective.•Theoretical frameworks are rarely used to guide process evaluations of MI. To explore how process evaluations were conducted alongside randomised controlled trials (RCTs) involving motivational interviewing (MI) as an intervention to manage health conditions. A scoping review was conducted. We searched 7 databases (to May 2021) for studies that incorporated at least one aspect of process evaluation of RCTs using MI to manage a health condition. Two reviewers screened the studies for eligibility and extracted data according to Medical Research Council framework. Of the 123 studies included, 85% lacked a theoretical framework for process evaluation. Most studies reported fidelity, but dose was underreported. Sixty-five studies reported mechanism of impact, but only twelve used participant experiences to understand how MI works. Only thirty used true mediation analysis. Context (n = 33) was the least reported aspect of process evaluation. Process evaluations of MI to manage health conditions often consist of fragmented reports of implementation, mechanisms, and context. Using validated measures of fidelity, reporting dose, and using mediation analysis alongside qualitative exploration of participant and stakeholder insights will improve our understanding of how MI works. Robust and comprehensive process evaluations will inform MI researchers to design more rigorous trials and for clinicians to implement more effective interventions for their clients.