Objectives To demonstrate that employing a mental health pharmacist in child and adolescent mental health services can significantly reduce medication expenditure, while assisting optimising medication use.

Method The financial evaluation was undertaken by comparing annual expenditure on medication between years 2004–2005 and 2014–2015, and examining any financial impact arising from the employment of the first pharmacist in 2007–2008. The current postholder and the chief pharmacist identified expenditure reduction initiatives undertaken or led by the pharmacist and agreed which key medicines optimisation roles the postholder had also undertaken.

Results Prior to the appointment of the pharmacist, annual drug expenditure over the preceding 3 years had remained steady at approximately £250 000. Since the first appointment in 2007, there has been a gradual and sustained reduction in expenditure and by March 2015, the annual reduction from baseline was approximately £133 000. This is significantly more than the £36 000 per annum that it cost to employ the pharmacist for six sessions a week and represents a net saving of £97 000 per annum. Eight key expenditure reduction initiatives were identified that were introduced and facilitated by the pharmacist.

Conclusions The period covered by this naturalistic evaluation was unusually stable with regard to the range and model of services provided, prescribing practice, medication prices and the medications available. It provided a rare opportunity to assess the financial impact of employing a pharmacist. These savings were pivotal in persuading Sussex Partnership NHS Foundation Trust to invest another £200 000 in 2016 in the employment of four additional pharmacists to work with the trust's community adult mental health teams.