Introduction: Electronic prescribing (ePrescribing) systems are rapidly being introduced into National Health Systems (NHS) hospitals in England following their widespread earlier adoption into primary care settings. Such systems require substantial changes in the way pharmacists organise their work and perform their roles. There is however as yet limited evidence on the extent to which these changes may support or compromise efficient and safe working practices by pharmacists. Identifying and quantifying these changes, and their effects, is central to informing system and work practice design, as well as informing training and implementation processes. This protocol describes a study to measure the impact of ePrescribing systems on pharmacists' time and workflow. Methods and analysis: A direct observational controlled pre-post implementation time-and-motion study will be conducted in six wards at one NHS Trust over two observational periods. Pharmacists will be shadowed and details of all work tasks performed will be collected and time-stamped. Task distribution, frequency and duration will be measured and changes in these measures preimplementation and postimplementation, and between control and intervention wards will be measured. Interviews with pharmacists will investigate their perceptions of the impact of the ePrescribing systems on their work and will be conducted in both periods. The extent to which pharmacists' expectations of the impact of the ePrescribing systems on their work with postimplementation reports will be qualitatively explored, as will any differences between perceptions and results from the time-and-motion analysis. Ethics and dissemination: Institutional research ethics approval has been obtained from The University of Edinburgh. Local approval from the participating NHS Trust and informed consent from participating pharmacists have been obtained, while also complying with local governance requirements. The results of the study will be presented at conferences, published in peer-reviewed journals, and shared with members of our Patient and Public Involvement Group, to facilitate wider dissemination.