Background and purpose: Experimental approach: The efficacy and safety of APE in asymptomatic or mildly symptomatic COVID-19 patients compared with placebo were investigated through a prospective, double-blind randomized control trial. Patients received APE containing 60 mg of andrographolide, three times a day for five days. WHO progression scale, COVID-19 symptoms, and global assessment evaluated the efficacy and adverse events, liver and renal functions were monitored for safety. Findings/Results: 165 patients completed the study (83 patients in the APE group and 82 patients in the placebo group). The highest WHO progression scale was 4 and COVID-19 symptoms were significantly relieved on the last day of intervention in both groups, with no significant difference between groups. APE significantly relieved headache symptoms on day 1 and olfactory loss symptoms on day 2 compared to placebo. The global assessment showed that 80.7% of patients had total recovery after 5-day treatment with APE. Mild diarrhea was the most common side effect with a high dose that resolved within a few days. No hepatic or renal toxicity was associated with treatment. Conclusion and implications: APE at 180 mg/day for 5 days did not reduce COVID-19 progression in asymptomatic or mildly afflicted COVID-19 patients, however, it shortened the symptoms of olfactory loss with no adverse effects over 5 days of use.