Exploring the factors influencing pharmacists' therapeutic reasoning in decision-making: a concurrent think aloud and semi-structured interview study

INTRODUCTION: Models of therapeutic reasoning conceptualize how pharmacists apply knowledge to weigh the benefits and risks of treatment options for patients but provide limited detail on the specific factors considered during the process. AIM: To explore the factors that prescribing pharmacists consider during therapeutic reasoning when making treatment decisions and how those factors are structured hierarchically. METHOD: This qualitative study explored the therapeutic reasoning of eight prescribing pharmacists as they worked through three primary care cases selected from hypertension, diabetes, heart failure and pediatric fever. Participants completed a think-aloud protocol to verbalize their thoughts in real time, a post-encounter form to promote reflection, and a semi-structured interview to clarify and elicit additional reasoning considerations. Data were audio-recorded, transcribed, and analyzed using template analysis. Each template iteration was critically reviewed by the research team with a detailed audit trail. Information power was reached at 18 cases (six pharmacists), with the remainder used for confirmation. RESULTS: We identified 35 factors across five themes: treatment planning, evidence and experience, drug-related factors, patient-centered factors, and setting influences. Therapeutic reasoning typically started with treatment planning to list broad options available in context and rule out options based on contraindications, cost and coverage. The remaining tailored list of options were evaluated using a non-linear process informed by evidence and experience, drug-related factors, and patient-centered factors. Setting influences, such as external pressures, access to clinical decision support systems, or the preferences of other clinicians influenced how the pharmacist considered treatment options. In total, 11 factors were associated with ruling out options, while the remaining factors informed the relative ranking of viable alternatives. Two levels of reasoning were observed: generic reasoning (case-independent) which relied on knowledge alone and patient-specific reasoning where relevant knowledge was applied to the patient case. Dynamic prioritization was observed as factor importance varied by case. CONCLUSION: This study advances the conceptualization of therapeutic reasoning by specifying the factors and their functional roles within decision-making. These findings provide a practical foundation for teaching, assessing, and supporting structured clinical decision-making in pharmacy practice.