OBJECTIVE: To investigate whether the mental health accreditation program drives improvements in the clinical practice of giving pro re nata (PRN) antipsychotic medications for psychiatric inpatients. METHODS: This study was conducted in October 2012, a record-based pre-post assessment design in psychiatric inpatient wards at King Khalid University Hospital, Riyadh, Saudi ArabiData collected from a 12-month pre-accreditation period (July 2009 to June 2010) was compared with those from a 12-month post-accreditation period (July 2011 to June 2012). The collected data identified demographics, diagnosis, number of PRN antipsychotic medications administered per patient, and indications for use. RESULTS: There were 177 patients during the pre-accreditation period, and 182 patients during the post-accreditation period. Before accreditation, 87% of patients were administered PRN antipsychotics and the average number of PRN antipsychotic administrations per patient was 12.10+/-7.0 compared with 81% of patients being administered 7.47+/-3.2 PRN antipsychotic medications per patient post-accreditation. Prior to accreditation, a high number of PRN antipsychotic medications were administered to patients with no specified indications (rs=0.698; p<0.001). During the post-accreditation period, the corresponding correlation coefficients significantly declined to rs=0.465; p<0.001. CONCLUSION: Implementation of clinical practice guidelines in psychiatric inpatients significantly reduces the frequency of PRN antipsychotic medications and enhances patient safety.