This prospective cohort study of 1,503 patients sought to identify timepoints during the inpatient hospitalization when pharmacists have the greatest potential for reducing medication errors. The study included 1,153 medication errors considered preventable and either moderate or severe. The majority (70%) of medication errors were identified during or before the first inpatient admission review by the pharmacist, suggesting that the greatest need for medication error identification and resolution is during the early stages of the hospital admission. However, the  study also identified that medication errors continue throughout the hospital stay, indicating a need for ongoing pharmacy review.