Medication prescribing errors are common in teaching hospitals. This study used critical incident debriefing to examine the underlying causes of why doctors—particularly trainees—make incorrect prescribing decisions. The team dynamic emerged as a significant factor in prescribing, with residents reporting being strongly influenced by other team members in both positive and negative ways. In particular, the authority gradient resulted in residents feeling unable to question senior physicians about prescribing decisions, but residents also reported receiving pressure from nurses to prescribe certain medications. Residents were also reluctant to change prescriptions written by colleagues for fear of creating team disharmony, even when they had concerns about the safety of the medication. While much research has focused on educational and technological solutions for prescribing errors, this study demonstrates a possible role for teamwork training.