BACKGROUND: Functional dyspepsia (FD) is a common gastrointestinal disease that is highly prevalent worldwide. Because of its heterogeneous pathophysiology, treatment options for FD can be difficult to choose; in this context, complementary and alternative medicine modalities have been suggested as promising options. AIM: To evaluate the efficacy of a traditional Persian medicine, jollab, in reducing patients' FD symptoms. METHODS: In a double-blind randomized clinical trial, 160 patients with a diagnosis of FD were enrolled and treated with either jollab or placebo (15ml, t.i.d., four weeks, orally). The outcomes reported were changes in symptom frequency and severity as recorded in patients' diaries and evaluated with the Short Form of the Leeds Dyspepsia Questionnaire (SF-LDQ), and physical examination. RESULTS: The response rate was higher in the treatment group (78%) than in the placebo group (31%) according to per-protocol sample analysis (P < .001). Symptoms of FD disappeared significantly more frequently, and the rate of concomitant synthetic drug consumption was significantly lower, in the jollab group compared to the placebo group at the end of the trial. Mean total symptom frequency and severity according to the SF-LDQ score was 1.55 ± 2.78 in the treatment group versus 5.61 ± 3.80 in the placebo group at the last follow-up time point (P < .001). A promising safety profile for jollab was observed throughout the trial. CONCLUSIONS: In patients with FD, jollab appeared to be more effective than the placebo. Complementary and alternative therapies such as the use of this traditional medicinal substance may be beneficial in relieving symptoms of dyspepsia [ACTRN12613000584730].