Pro re nata (PRN) or 'as required' medication is a regular part of mental health nursing practice. This retrospective study accessed data recorded for all PRN being given to patients within an eight-bed psychiatric intensive care unit. Data from the same consecutive 4-month period from 2005 and from 2007-2009 were analysed for trends in overall rates, time of administration, and type of medication given. PRN administration was identified to each patient, but no demographic information was analysed. Results of this study demonstrated a gradual decline in the total number of PRN given, reducing from an average of 314 PRN per month in 2005, to 181 PRN per month in 2009. The typical number of patients per month receiving any PRN did not change, with 41 out of a total of 72 patients receiving at least one PRN in 2005, and 40 out of 64 patients receiving PRN in 2009. These results suggest that over the study timeframe, nurses became more selective as to which patients received PRN. This discussion examined the possible reasons for this result, including unit leadership style, changes in staffing levels, a new nursing model and group programme, and the relocation to a new facility.