Multiphase Optimization Implementation Strategy for Tobacco Cessation Interventions in Primary Care Clinics: A Cluster-Randomized Type 3 Hybrid Effectiveness-Implementation Trial

Background Background: Brief verbal Intervention for Smoking Cessation (BISC) is an evidence-based practice proven to be effective and cost-efficient, yet its implementation in primary healthcare (PHC) clinics in China is currently inadequate. Developing and evaluating multifaceted implementation strategies are crucial to translating such evidence-based practices into routine clinical care. This study protocol outlines a rigorous, multi-phase approach to identifying and testing the most effective strategies for BISC implementation. Method This is a two-phase study utilizing the Multiphase Optimization Strategy (MOST) . The first phase, which has been completed, involved using a scoping review, stakeholder consultations, and a Best-Worst Scaling (BWS) online survey to systematically identify and define four key implementation strategies. The second phase will be a cluster-randomized 2×2×2 factorial trial designed to ascertain the optimal combination of these strategies. The study's outcomes are categorized into a primary aim (implementation outcomes) and a secondary aim (patient outcomes), with objective measurement facilitated by the use of Unannounced Standardized Patients (USPs). Discussion This protocol outlines the utilization of the MOST framework to customize the optimized combination of implementation techniques for BISC within the local context. By using a factorial design, the study will be able to unpack the black box of multi-component interventions and identify which specific components are most effective and efficient. This approach is expected to provide a valuable methodological paradigm for advancing implementation science in low- and middle-income countries.