Background and aim. The study aimed to assess the efficacy of the treatment of Kan Jang®, a fixed combination of Andrographis paniculata (Burm. F.) Wall. ex. Nees and Eleutherococcus senticosus (Rupr. & Maxim.) Maxim in patients with mild symptoms of COVID-19. Methods. One hundred forty patients received six capsules of Kan Jang® (n = 68, daily dose of andrographolides – 90 mg) or placebo (n=72) and supportive treatment (paracetamol) for 14 consecutive days in a randomized, quadruple-blinded, placebo-controlled, two-parallel-group design. The efficacy outcomes were the rate of cases turning to severe, the detection rate of SARS-CoV-2 virus over the time of treatment, the duration and the severity of symptoms (sore throat, runny nose, cough, headache, fatigue, loss of smell, taste, pain in muscles) in the acute phase of the disease. Other efficacy measures included improving cognitive and physical performance, quality of life, and the levels of inflammatory blood markers - IL-6, c-reactive protein, and D-dimer. Results. Kan Jang® significantly (p < 0.05) reduced the rate of cases turning to severe (5.36%) compared to placebo (17.86%) and decreased the detection rate of SARS-CoV-2 virus over the time of treatment. The statistical difference in the rates of patients with clinical deterioration in the Kan Jang treatment and placebo control groups was significant (p = 0.0176) both in 112 patients included per protocol (IPP) analysis and in 140 patients included per intention to treat (ITT) analysis (p = 0.0236); the absolute risk reduction of cases by Kan Jang treatment was 12.5%, and the number Needed to Treat by Kan Jang was 8. The patient's recovery time (Number of sick days at the home/clinic) was shorter in the Kan Jang group compared with the placebo group. The rate of resolution of inflammatory symptoms in the Kan Jang® group was significantly higher compared with the placebo group, and relief of the severity of cough, sore throat/pain, runny nose, and muscle soreness. Kan Jang® significantly decreased the Wisconsin Upper Respiratory Symptoms scores compared to placebo in the sample size of 140 patients. However, the relief of fatigue and headache and the decrease of IL-6 in the blood was observed only in a subset of the 86 patients infected during the second three waves of the pandemic. Kan Jang® significantly increased physical activity and workout; however, it did not affect cognitive functions (attention and memory), Quality of life Score, inflammatory markers D-dimer, and c-reactive protein compared with the placebo group. Conclusions. Overall, the results of this study suggest that Kan Jang® is effective in treating mild and moderate COVID-19 irrespective of SARS-Cov-2 variants infection.