Background/Aims: The treatment of refractory functional dyspepsia (FD) is a challenge. Clidinium/chlordiazepoxide is a combination of antispasmodic and anxiolytic drugs that has been used as an adjunct treatment for FD in clinical practice with limited supporting evidence of efficacy. The aim of the study is to assess the efficacy and safety of clidinium/chlordiazepoxide as an adjunct treatment to a proton pump inhibitor (PPI) in refractory dyspepsia. Methods: We performed a study of patients who met the Rome IV criteria for FD who failed to respond to PPIs. Patients were randomly assigned to groups that received clidinium/chlordiazepoxide or placebo as an add-on treatment to PPI for 4 weeks. The primary outcome was the rate of responders, which was defined as a > 50% reduction in dyspepsia symptom score after 4 weeks of treatment. The secondary outcomes were an improvement in the quality of life and the safety profile. Results: Between March 2017 and February 2018, 78 patients were enrolled. The rates of responders in the clidinium/chlordiazepoxide group and placebo groups were 41.03 % and 5.13% at week 4 (P < 0.001). The clidinium/chlordiazepoxide group also showed significant improvement in overall quality of life over placebo. However, the clidinium/chlordiazepoxide group had more frequent drowsiness than the placebo group (30.27% vs 6.52%, P = 0.034). There were no major adverse events in either group. Conclusions Clidinium/chlordiazepoxide significantly improved dyspeptic symptoms and quality of life. This combination may be used as an add-on therapy in FD patients without major adverse events.