IntroductionBy implementation of Enhanced Recovery After Bariatric Surgery protocols and day-care surgery, early discharge poses a challenge if excessive bleeding occurs after bariatric surgery. Tranexamic acid (TXA) has demonstrated efficacy in other surgical fields and in bariatric pilot studies. This trial aims to assess the efficacy of peroperative administration of TXA in reducing haemorrhage in patients undergoing gastric bypass surgery.Method and analysisThis is a multicentre, phase III, double-blind randomised controlled trial in six high-volume bariatric centres in the Netherlands. A total of 1524 eligible patients, aged 18 years or older, undergoing primary gastric bypass surgery (either Roux-en-Y gastric bypass or one-anastomosis gastric bypass) will be randomised between TXA and placebo (1:1, variable block, stratified for centre, day-care/overnight stay and type of surgery) after obtaining informed consent (2.5% less haemorrhage, power 80%, 2-sided-α 0.05 and 10% dropout). Exclusion criteria are pregnancy, amedical history of acute bleeding (without cause), venous thrombotic events (VTEs), epilepsy, anticoagulant use and iatrogenic bleeding during surgery (aside from staple line). The primary outcome is postoperative haemorrhage requiring intervention within 30 days postoperatively. Secondary outcome measures are staple line reinforcement, blood loss, duration of surgery, postoperative haemoglobin, vital parameters, minor and major complications, side effects of TXA (nausea, hypotension and VTE), length of hospital stay and directly made costs.Ethics and disseminationWritten informed consent will be obtained from all participants. The protocol has been approved by the Medical Research Ethics Committees United, Nieuwegein, on 7 February 2023 (registration number: R22.102). Results will be disseminated through peer-reviewed publications and conferences.Trial registration numberNCT05464394