Poor practice associated with pro re nata (PRN) prescriptions in mental health is known to be common and can increase the risk of serious and potentially fatal side effects. A contributing factor to poor practice is the lack of a clear chain of accountability between the decision to prescribe and administer PRN prescriptions. To address this problem, a patient group direction (PGD) for acute behavioural disturbance (lorazepam 0.5–2 mg) and staff training materials were developed. The intention was to replace PRN prescriptions with the PGD in two mental health trusts. One of the potential benefits of this would be the removal of the contribution of PRN to high and combined dose antipsychotic prescriptions. This proposal, however, was met with significant resistance in both trusts and did not replace PRN as a result. A series of interviews and focus groups were conducted with 16 RMNs working in the two trusts, to explore the reasons why the PGD was met with resistance. Senior nurses perceived resistance to be associated with anxieties over increased responsibility for decision making. Junior nurses reported concerns regarding the medicalization of the nursing role, the paperwork associated with the PGD and the training approach used. Future efforts to implement PGDs in mental health settings must carefully consider the methods for engaging effectively with participating organizations, in terms of managing change and completing the necessary groundwork for successful implementation.