Background Medication dispensing errors cause wastage of medicines and increase healthcare costs, with serious consequences for patients. However, few studies have systematically and completely reviewed dispensing errors, with inadequate attention to the objective regularity and risk factors for dispensing errors.

Objectives To explore the potential causes and risk factors influencing the prevalence of medication dispensing errors.

Methods We collected patient-reported medication dispensing errors from a large tertiary care hospital in South China over 11 years. We assessed the characteristics of dispensing errors, labelled the causes, compared them with more than 25 million prescriptions from 2012 to 2022, identified the susceptibility factors for the occurrence of dispensing errors, and analysed the characteristics and patterns of the errors.

Results A total of 376 patient-reported dispensing errors were recorded. It took an average of 5.2 days for a patient to find an error. Only 37.5% of errors were reviewed by the patient within 24 hours. These errors directly contributed to a medication loss of US$188 406. Of the 160 recorded pharmacists, 112 (70%) committed dispensing errors. Dispensing errors were affected by the pharmacists’ use of the machine, workload and the length of monthly vacation. Of the dispensing errors, 47.9% (n=180) were caused by medication packaging or names that were similar. Antibiotics (n=32, 8.5%) were the most common types of drugs dispensed incorrectly, and traditional Chinese medicines (n=31, 8.2%) and immunosuppressants (n=21, 5.6%) were the most likely to be dispensed in inaccurate quantities.

Conclusions Organising adequate staff and using machines to prepare medicines may be necessary to reduce dispensing errors. When pharmacists have been away from work for more than 72 hours they should find their rhythm in other positions before dispensing medicines. It is more important to prioritise the differentiation of medicines with similar packaging over those with similar names when arranging drug shelving.