Introduction - There is some evidence that homeopathic treatment has been used successfully in previous epidemics, and currently some countries are testing homeoprophylaxis for the coronavirus disease 2019 (COVID-19) pandemic. There is a strong tradition of homeopathic treatment in India: therefore, we decided to compare three different homeopathic medicines against placebo in prevention of COVID-19 infections. Methods - In this double-blind, cluster-randomized, placebo-controlled, four parallel arms, community-based, clinical trial, a 20,000-person sample of the population residing in Ward Number 57 of the Tangra area, Kolkata, was randomized in a 1:1:1:1 ratio of clusters to receive one of three homeopathic medicines (Bryonia alba 30cH, Gelsemium sempervirens 30cH, Phosphorus 30cH) or identical-looking placebo, for 3 (children) or 6 (adults) days. All the participants, who were aged 5 to 75 years, received ascorbic acid (vitamin C) tablets of 500 mg, once per day for 6 days. In addition, instructions on healthy diet and general hygienic measures, including hand washing, social distancing and proper use of mask and gloves, were given to all the participants. Results - No new confirmed COVID-19 cases were diagnosed in the target population during the follow-up timeframe of 1 month—December 20, 2020 to January 19, 2021—thus making the trial inconclusive. The Phosphorus group had the least exposure to COVID-19 compared with the other groups. In comparison with placebo, the occurrence of unconfirmed COVID-19 cases was significantly less in the Phosphorus group (week 1: odds ratio [OR], 0.1; 95% confidence interval [CI], 0.06 to 0.16; week 2: OR, 0.004; 95% CI, 0.0002 to 0.06; week 3: OR, 0.007; 95% CI, 0.0004 to 0.11; week 4: OR, 0.009; 95% CI, 0.0006 to 0.14), but not in the Bryonia or Gelsemium groups. Conclusion - Overall, the trial was inconclusive. The possible effect exerted by Phosphorus necessitates further investigation.