In this article, we describe a multi-year writing intervention in a highenrollment professional pharmacy course, implemented by a multidisciplinary team of pharmacy and writing instructors. Built around one capstone writing assignment, the "drug information question" paper, the intervention was designed to specifically improve students' writing and health science reasoning skills and their overall scores in the course, since historically students scored low on this assignment. We provide a background of our pharmacy program and an overview of writing in pharmacy, describe the history of the intervention and collaboration between pharmacy and writing faculty, and explain the design and principles of the intervention, the results, and the implications of the study for STEM writing pedagogy. Over the course of four years, starting with a peer-review model, we have gradually added lectures, workshops, and optional and mandatory Writing Center sessions in an effort to improve students' learning and health science reasoning skills. Over the same period of time, student scores on their written capstone in the course improved significantly, and survey results indicated that the students viewed the peer review process and the writing program interventions favorably.