Functional dyspepsia (FD) is characterized by one or more symptoms, including epigastric pain, burning, early satiety, and postprandial fullness, occurring in the absence of identifiable structural abnormalities on imaging or endoscopy. Symptomatic improvement with pharmacological treatment is often unsatisfactory due to the heterogeneous nature of the condition.This study evaluated the efficacy of a green tea seed and leaf extract complex (TSL) in alleviating symptoms of FD.Eligible participants were adults aged 19–70 years who presented with at least one of the four FD symptoms defined by the ROME IV criteria and showed no structural abnormalities on upper gastrointestinal endoscopy. In a double-blind, randomized, placebo-controlled trial, 100 adults with FD were assigned to receive either TSL (n = 50) or placebo (n = 50) at a dose of 500 mg/day for 8 weeks.The primary endpoint was the change in total score on the Gastrointestinal Symptom Rating Scale (GSRS). The TSL group demonstrated a significantly greater improvement in total score compared with the placebo group (-5.73 ± 6.27 vs. -2.02 ± 7.09, P = 0.0148). Analysis of changes in individual GSRS symptom scores revealed that, at the 8-week follow-up, reflux (−1.02 ± 1.27, P < 0.0001) and abdominal pain (−1.12 ± 2.14, P = 0.0017) significantly decreased in the TSL group compared with baseline. No significant differences were observed between groups in the incidence of severe adverse events (AEs), and all AEs were deemed unrelated to the study materials.Previous research has indicated that catechins found in green tea leaves, particularly epigallocatechin-3-gallate (EGCG), exert anti-inflammatory and antioxidant effects by interacting with cell membrane receptors, modulating intracellular signaling pathways, and influencing nuclear transcription regulators. Collectively, these findings suggest that the improvement in FD symptoms observed in the present study may be attributed to the multiple anti-inflammatory mechanisms of green tea.In conclusion, various gastrointestinal symptoms improved after 8 weeks of administration of 500 mg TSL in adults with FD, without severe AEs. Our findings indicate that TSL may be an effective and safe alternative for managing symptoms in adults with FD.