Hospital electronic prescribing and medicines administration (HEPMA) system implementation is advocated by national e-health strategies to produce patient safety benefits. No previous study has evaluated HEPMA implementation impacting discharge information communication or assessed discharge prescribing errors. The aims were to assess HEPMA system implementation impact on medicines related discharge communication and prescribing errors, and to gain the perspective of hospital staff involved in the communication process. Following a narrative literature review, a convergent parallel mixed methods was selected, consisting of interpretative phenomenology and experimental before and after study design. Face-to-face semi-structured interviews of a purposive sample of hospital staff involved in discharge information communication were undertaken using the Theoretical Domains Framework (TDF) as a theoretical lens. In addition a quasi experimental retrospective case notes review, both before and after implementation was completed. Pre-implementation, staff described patient safety concerns with traditional discharge communication processes. They cited frequent prescribing errors, and associated adverse events and hospital readmissions. HEPMA implementation was anticipated to improve patient safety and create more efficient discharge communication. Post-implementation staff articulated improved information quality highlighting fewer omitted medicines and improved patient safety. TDF findings of behaviour change highlighted behavioural alteration including adaption of processes to improve discharge quality. Quantitative data collection (n=159 before and after) confirmed qualitative findings; increased compliance with discharge documentation, for example staff grade recorded increased from 40% to 100% (p<0.001). Prescribing error quantity and severity were reduced; errors reduced from 99% to 23% of patients (p<0.001); only 22% of identified errors likely to cause harm. Omitted medicines decreased from 42% to 11% of patients (p<0.001). The findings contribute original knowledge concerning HEPMA implementation impacting discharge information communication and prescribing errors. The study demonstrated reduced prescribing errors and improved patient safety which potentially impacted health and wellbeing. Qualitative findings and quantitative results are transferable and applicable to other NHS organisations or similar healthcare settings.