To explore behavioural determinants influencing General Practitioner (GP)-led medication reconciliation (MedRec) and inform the development of a theory-informed implementation strategy tailored to the primary care context.

Despite national and international recommendations endorsing MedRec to reduce medication errors, its consistent implementation in primary care remains limited.

We conducted a qualitative study involving GPs working in the largest Health Region in Portugal, building on findings from preceding quantitative studies. Data were analysed using a Theoretical Domains Framework (TDF)-informed approach. Key determinants were mapped to intervention functions using the Behaviour Change Wheel (BCW), and candidate behavioural change techniques (BCTs) were subsequently proposed.

A total of 22 GPs participated in three focus group discussions. The ‘Environmental context and resources’ domain gathered the most coded segments, related to patients, other health professionals, electronic health records, and time constraints, mainly reflecting perceived barriers. ‘Knowledge’ and ‘Skills’ emerged as key domains, with ambiguity in the MedRec definition undermining its explicit recognition and influencing other domains. Facilitators included GPs’ commitment to patient safety aligned with GPs’ professional role. The interplay between barriers and facilitators suggested a cascading effect across domains. Candidate BCTs proposed to address these determinants included feedback on behaviour/outcomes, self-monitoring, prompts/cues, restructuring and adding objects to the environment. This study provides a theory-informed foundation for designing tailored implementation strategies to support MedRec practices in Portuguese primary care. Future work should focus on assessing the appropriateness, feasibility and acceptability of the proposed BCTs within the constraints of real-world primary care settings.