Purpose: Medical students often struggle to translate pharmacological knowledge into clinical reasoning, contributing to perceived unpreparedness for clerkships. To address this, we developed case-based multiple-choice questions (MCQs) requiring written pharmacological justification, embedded within weekly formative essays. Methods: Few interventions combine rationale-based MCQs with written justification in a formative essay format. This approach could promote critical analysis, broadened content exposure, and practice in a format mirroring USMLE Step 1, with detailed rationales for all options as immediate feedback. Over ten weeks, 100 first-year medical students completed 44 rationale-based MCQs spanning cardiovascular, pulmonary, and renal pharmacology. This descriptive, mixed-methods study evaluated Kirkpatrick Level 1 (satisfaction) and Level 2a (attitude modification) outcomes using Likert-scale and open-ended survey items. Results: End-of-course evaluations (n=97) revealed positive student perceptions: 84.5% agreed the MCQs connected pharmacology concepts across learning activities, 85.6% reported improved application of principles to clinical decision-making, and 86.6% noted enhanced retention over time. Qualitative feedback indicated concerns regarding perceived increased workload and the relevance of certain topics not directly covered in lectures. However, students valued the detailed explanations and USMLE Step 1 preparation. Conclusion: This intervention demonstrates the potential of rationale-based MCQs to foster clinical reasoning, deepen pharmacological understanding, and provide self-assessment opportunities in pre-clerkship medical education. Limitations include absence of a control group and reliance on self-reported perceptions rather than objective performance outcomes.