Successful team care requires a shared understanding of roles and expertise. This paper describes the development and preliminary exploration of the psychometric properties of a tool designed to measure contributions to family practice medication-related processes. Our team identified medication-related processes commonly occurring in family practice. We assessed clinical appropriateness using a sensibility questionnaire and pilot-tested with 11 pharmacists, nurses and physicians. We performed a simulated exercise to group the processes and assessed the internal consistency of the groupings using Cronbach's alpha coefficient. We examined test-retest reliability using intra-class coefficient (ICC). Following three revisions, the final Medication Use Processes Matrix (MUPM) included 22 medication-related processes and scale descriptors reflecting contribution to each process. Mean sensibility ratings were high for each component. We developed five theoretical groupings (diagnosis & prescribing, monitoring, administrative/documentation, education, medication review) and found their overall internal consistency was good (alpha > 0.80). The test-retest reliability was strong (ICC > 0.80). Preliminary validation showed significant differences in how health professionals view interprofessional contributions toward medication-related processes. Interprofessional care requires a negotiated understanding of processes and contributions. The MUPM provides an explicit description of medication-related processes in primary care, measures perceived contributions and emerges as a new tool to measure collaborative care in family practices.