BackgroundConducting high-quality randomized clinical trials (RCTs) is challenging, time consuming, and resource intense. Academic investigators usually depend on scarce financial resources; however, current literature lacks systematically collected empirical data on the detailed resource use and costs of investigator-initiated RCTs.MethodsThe aim of this study is to generate a database of detailed empirical resource use and cost data from 100 investigator-initiated RCTs in Switzerland, Germany, and the UK. Investigators enter their empirical costs data into an online data collection form, which is followed by a short interview and a detailed cost report. We plan to investigate cost patterns and cost drivers and examine planned versus actual RCT costs as well as explore different strata of costs across the planning, conduct, and finalization phases, in drug and non-drug trials, and across medical fields and countries.DiscussionThis study will add detailed empirical data to the limited research on investigator-initiated RCT costs currently available. A study limitation will be that cost data will be retrospective and self-reported, which might be inaccurate depending on how costs were recorded.Trial registrationOpen Science Framework (OSF) https://doi.org/10.17605/OSF.IO/QY2GU. Registered on June 4, 2021.