ObjectiveThis clinical trial aimed to evaluate the efficacy and safety of Jiandu granule, a Chinese herbal medicine formula, for preventing oral mucositis in patients with nasopharyngeal carcinoma undergoing concurrent chemoradiotherapy.Materials and MethodsA single-centre, open-label, randomised controlled trial was conducted, enrolling 138 patients with locally advanced nasopharyngeal carcinoma. Patients were randomly allocated to either the experimental group (n = 69) or the control group (n = 69). Both groups received concurrent chemoradiotherapy and standard care for oral mucositis, with the experimental group additionally receiving Jiandu granule intervention. The primary outcome was the incidence of severe oral mucositis (grade III to IV).ResultsIn the full-analysis set, severe oral mucositis occurred in 14 of 69 (20.3%) patients in the experimental group and 31 of 69 (44.9%) patients in the control group (absolute risk reduction: 24.6%; relative risk reduction: 54.8%; p = 0.002; number needed to treat: 4). Jiandu granule was associated with mild/moderate gastrointestinal reactions, with an overall incidence of 5.9%.ConclusionJiandu granule reduced the incidence of severe oral mucositis in nasopharyngeal carcinoma patients during concurrent chemoradiotherapy and had an acceptable safety profile.