Incidences of infections with Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) are still high and treatment guidelines lack specific recommendations for outpatients with Coronavirus-induced disease 2019 (COVID-19). Phytomedicine ELOM-080, an enhancer of mucociliary clearance (MCC), showed benefits as add-on therapy in hospitalised COVID-19 patients. This randomised, double-blind, placebo-controlled proof-of-concept study investigated whether outpatients with mild to moderate acute symptomatic COVID-19 would benefit from a 14-day treatment with ELOM-080 with regard to potential early treatment effects on cough and further typical COVID-19 symptoms. Outpatients with mild to moderate acute symptomatic COVID-19 documented symptom severity and count of coughs on a daily basis. Investigators documented safety and symptom severity during the visits. This study missed its primary objective, which was reduction in coughing fits in comparison to placebo treatment. In primary analysis, no relevant differences were observed between treatment arms. Data for all randomised patients showed broad heterogeneity in, e.g., time courses of coughing fits, which affected both magnitude and timing of the changes from baseline. However, post hoc analyses with a population with suspected dysfunctional MCC revealed that patients significantly benefitted from treatment with ELOM-080 in terms of reduction in coughing fits (p = 0.0070), difficulty breathing on exertion (p = 0.0252), and earlier remission of symptoms by 1-3 days. We have shown that patients with dysfunctional MCC benefit from treatment with ELOM-080. These results might be of clinical importance, as up to now no therapy has obtained market approval for the treatment of outpatients with COVID-19. EudraCT number: 2022-003478-22.