Implementation science in hybrid randomised controlled trials: a state-of-the-art systematic review

Introduction: Hybrid randomised controlled trials (RCTs) combine effectiveness and implementation aims to accelerate evidence translation. Being a new yet evolving methodology, it is timely to review the characteristics and reporting quality of hybrid RCTs, and how implementation science theories, models and frameworks (TMFs) were used.Methods: Citation-indexed databases were searched from 2012 (inception of “hybrid” terminology) to 2025 for RCTs that identified as “hybrid” in the title/abstract/keywords and cited and applied a TMF. RCT design and implementation characteristics were extracted. Reporting quality assessment followed the Standards for Reporting Implementation Studies.Results: Of 1864 initial hits, 111 papers were included, comprising 52 main results papers, 37 protocol papers and 22 secondary results papers. Most RCTs were published in the past five years (79%), conducted in North America (62%), in primary care/community settings (50%), and calculated sample sizes using the clinical effectiveness outcome (64%). TMFs were more often used to inform implementation outcomes (88%) compared to implementation strategies (52%). The most common TMFs were the Reach, Effectiveness, Adoption, Implementation, Maintenance Framework (44%) and Proctor et al.’s taxonomy of implementation outcomes (29%). Reporting quality was stronger for clinical intervention components, with fewer RCTs reporting the rationale and fidelity of implementation strategies (27%) compared to the clinical intervention (60%).Conclusions: Hybrid RCTs that apply TMFs are increasing, yet there is evidence that maturation is warranted. Clinical effectiveness remains the focus for most hybrid RCTs rather than implementation. More deliberate application and reporting of implementation science TMFs may improve the quality of future hybrid RCTs.