Background: Previous studies on Deva-5 traditional prescription, which has long been used in traditional medicine for the treatment of influenza, have demonstrated inhibitory activity against influenza A (H3) virus and antimicrobial activity against Staphylococcus aureus. Based on this traditional formula, De-Mon syrup was developed through pharmaceutical processing. Experimental studies have shown that this syrup possesses anti-inflammatory properties. Therefore, conducting a clinical study to evaluate its therapeutic effect in influenza is warranted. Aim: To investigate the anti-inflammatory effect of De-Mon syrup, derived from a traditional herbal formulation, in patients with influenza. Materials and Methods: A randomized controlled clinical trial with a parallel design was conducted among 160 patients diagnosed with influenza (ICD-10: J09–J11) who met the inclusion criteria. Participants were randomly assigned into two groups. The treatment group received standard influenza therapy with oseltamivir combined with De-Mon syrup, administered four times daily for five days at age-appropriate doses for children and adults. The control group received oseltamivir twice daily for five days. Complete blood count parameters were measured before and after treatment, and the results were statistically analyzed. Result: According to the study results, the adult treatment group demonstrated a statistically significant reduction in white blood cell and neutrophil counts compared with the control group (p<0.05). Similarly, when children in the treatment group were compared with those in the control group, white blood cell count, C-reactive protein levels, and neutrophil counts were significantly decreased, indicating statistically significant differences (p<0.05). Conclusion De-mon syrup, based on a traditional prescription, significantly reduced white blood cell count, C-reactive protein, and neutrophil levels in patients with influenza (p<0.05), indicating a potential anti-inflammatory effect.