Objective: Clinicians are increasingly being asked to implement guideline recommendations into their practice, but are given little practical guidance on this complex task. In this paper we outline a promising theory-driven approach we took to implementing guideline recommendations about routine monitoring of weight gain and metabolic disturbance in our first-episode psychosis clinic. While there is significant psychological and physical morbidity associated with weight gain and metabolic disturbance, routine monitoring was not being undertaken according to guideline recommendations. We examined the factors that make it difficult to undertake routine monitoring by interviewing psychiatrists. This barrier analysis allowed us to develop and introduce feasible and acceptable strategies to address these barriers, increasing the likelihood that routine monitoring would take place. Conclusion: This paper advocates for undertaking an analysis of the barriers clinicians face to undertaking evidence-based practice in order to develop more sophisticated approaches to address areas where clinical practice and evidence are divergent. Such an approach is more likely to ensure that measures to improve practice are successful, are meaningful for the clinicians involved, and become imbedded in the clinical practice of the service.