The purpose of this study was to investigate perceptions of barriers to safe administration of medicines in mental health settings. A cross-sectional survey was used, and 70 mental health nurses and 41 students were recruited from a mental health trust and a university in Yorkshire, UK. Respondents completed a questionnaire comprising closed- and open-response questions. One item, which contained seven sub-items, addressed barriers to safe administration of medication. Seven themes—five nurse- and prescriber-focused and two service user-focused—were abstracted from the data, depicting a range of barriers to safe administration of medicines. Nurse- and prescriber-focused themes included environmental distractions, insufficient pharmacological knowledge, poorly written and incomplete medication documentation, inability to calculate medication dosage correctly, and work-related pressure. Service user-focused themes comprised poor adherence to medication regimens, and cultural and linguistic communication barriers with service users. Tackling medication administration error is predominantly an organizational rather than individual practitioner responsibility.