Abstract Background Evidence demonstrates that measures are needed to optimise therapy and improve administration of medicines in care homes for older people. The aim of this study is to determine the clinical and cost effectiveness of a novel model of multi-professional medication review. Methods A cluster randomised controlled trial design, involving thirty care homes. In line with current practice in medication reviews, recruitment and consent will be sought from general practitioners and care homes, rather than individual residents. Care homes will be segmented according to size and resident mix and allocated to the intervention arm (15 homes) or control arm (15 homes) sequentially using minimisation. Intervention homes will receive a multi-professional medication review at baseline and at 6 months, with follow-up at 12 months. Control homes will receive usual care (support they currently receive from the National Health Service), with data collection at baseline and 12 months. The novelty of the intervention is a review of medications by a multi-disciplinary team. Primary outcome measures are number of falls and potentially inappropriate prescribing. Secondary outcome measures include medication costs, health care resource use, hospitalisations and mortality. The null hypothesis proposes no difference in primary outcomes between intervention and control patients. The primary outcome variable (number of falls) will be analysed using a linear mixed model, with the intervention specified as a fixed effect and care homes included as a random effect. Analyses will be at the level of the care home. The economic evaluation will estimate the cost-effectiveness of the intervention compared to usual care from a National Health Service and personal social services perspective. The study is not measuring the impact of the intervention on professional working relationships, the medicines culture in care homes or the generic health-related quality of life of residents. Discussion This study will establish the effectiveness of a new model of multi-professional clinical medication reviews in care homes, using novel approaches to recruitment and consent. It is the first study to undertake an examination of direct patient outcomes, together with an economic analysis. Trial Registration ISRCTN: ISRCTN90761620