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Introduction Preoperative administration of tranexamic acid (TXA) reduces perioperative blood loss and transfusion requirements in total hip arthroplasty (THA), but optimal dosing remains uncertain due to the narrow range of doses explored in prior studies. This study aims to define the dose–response of intravenous TXA in THA, focusing on perioperative haemoglobin drop to improve blood-sparing effect.Methods and analysis This monocentric, double-blind, placebo-controlled, parallel-group, dose-finding study will enrol 170 adults undergoing THA, aiming to randomise 150 patients. Participants will be allocated using a minimisation technique with a random component in equal proportions to receive either placebo or one of four intravenous TXA doses: 300 mg, 500 mg, 1000 mg or 3000 mg. Dose selection and sample size are based on a model-based meta-analysis that employed a maximum effect (Emax) model with a maximum effect of 40% and an ED50 (dose providing 50% of Emax) of 400 mg. The primary outcome will be the relative perioperative haemoglobin drop at postoperative day 3. Secondary outcomes include TXA exposure and perioperative fibrinolytic activity as measured by D-dimer levels. Only patients receiving the allocated study treatment will be analysed (modified intention-to-treat population). The dose–response relationship for the primary outcome will be analysed using non-linear mixed-effect models.Ethics and dissemination The study protocol was approved by the French ethics committee (Institutional Review Board Sud Méditerranée V) and the French National Agency for the Safety of Medicines and Health Products (ANSM). Results will be disseminated at conferences and published in peer-reviewed journals.Trial registration number CTIS 2022-502532-38-01; NCT03822793.