Introduction Behavioural and psychological symptoms of dementia (BPSD) should only rarely and briefly be treated with antipsychotics. Despite recommendations to the contrary, the use of antipsychotics in nursing home residents with dementia is widespread and followed by serious adverse effects. Intervention studies on methods to reduce the use of antipsychotics in persons with dementia are few and needed. The aim of this protocol is to describe the rationale and content of the intervention DEprescribing and Care to reduce Antipsychotics in DEmentia (DECADE)-a hybrid effectiveness-implementation pilot study. Materials and methods This is a protocol of a prospective hybrid effectiveness-implementation pilot study. The primary aim of DECADE is to reduce the use of antipsychotic drugs by 50% in 50% of nursing home residents with dementia while maintaining or improving BPSD. The intervention is implemented in six nursing homes including approximately 190 residents with dementia and consists of Academic Detailing, medication review, education of nursing home staff, and care plans. The evaluation of feasibility and potential effectiveness is an overall assessment of all clinical and process outcomes. Logistic regression analyses will be used to investigate factors characterizing situations with prescription of antipsychotics. BPSD is analysed with a before- and after design using self-controlled case series methods and the use of antipsychotics is analysed as interrupted time series. Discussion This protocol describes a study that will provide an indication of DECADE effectiveness and a model for upscaling and further evaluation in a controlled design.