John: Hello, I'm John Hilton, senior editor at Cochrane. Cochrane is producing a series of reviews relevant to the COVID-19 pandemic. In July 2021, we published the first version of our review on the effects of ivermectin for the prevention and treatment of COVID-19, in a collaboration between Cochrane's Infectious Diseases and Haematological Malignancy Groups. We asked one of the authors, Maria Popp from University Hospital Wuerzburg in Germany, to tell us about their findings.

Maria: Ivermectin is a commonly used drug to treat parasites, such as scabies in humans and intestinal worms in cattle. Before the COVID-19 pandemic, some studies had shown that, under laboratory conditions, it could inhibit the replication of viruses, such as the one responsible for dengue fever. In April 2020, similar laboratory tests suggested a weak inhibitory effect on SARS-CoV-2, which is the virus that causes COVID-19 and during 2020, more than 30 clinical trials started, to test ivermectin as a treatment for COVID-19. Several of the small, early trials suggested large mortality benefits, which led some advocacy groups to lobby for the widespread introduction of ivermectin across the world, and making it important to do a systematic review to bring all the evidence together in an unbiased way.
Therefore, funded by the German CEOsys project, we set out on our Cochrane Review of the effects of ivermectin in preventing and treating COVID-19 infection. We wanted to know if ivermectin can prevent the disease or if it reduces death, illness and length of infection in people who have it. We also looked for unwanted side effects of the drug.
We searched for randomized trials that investigated ivermectin to prevent or treat COVID-19 in humans. People being treated with ivermectin had to have laboratory-test confirmed COVID-19 and be receiving treatment in hospital or as outpatients. The studies needed to compare ivermectin to placebo, no treatment, usual care or a treatment for that was known to work to some extent for COVID-19. We excluded studies that compared ivermectin to other drugs that do not work, such as hydroxychloroquine, or drugs that are not known to be effective against COVID-19. 
We found one randomised trial for the prevention of COVID-19 that had recruited 156 people in Egypt, and 13 trials of treatment, with a total of approximately 1500 patients. For treatment, there were nine studies of people with moderate COVID-19 in hospital and four of outpatients with mild COVID-19. The studies used different doses of ivermectin and different durations of treatment. We also found 31 ongoing studies, and another 18 that are closed and not yet published or where we are seeking clarification from authors.
Our main finding is that we found no evidence to support the use of ivermectin for either preventing or treating COVID-19 infection. We cannot confirm if ivermectin, whether administered in hospital or as an outpatient, leads to more or fewer deaths after one month than a placebo or usual care. Further, we cannot confirm whether it improves or worsens patients' condition, increases or decreases unwanted side effects, or leads to more or fewer negative COVID-19 tests 7 days after treatment. Likewise, the evidence that is currently available for the review cannot confirm whether or not ivermectin prevents COVID-19 infection or reduces the number of deaths after high-risk exposure to the SARS-CoV-2 virus.
In summary, the current lack of good quality evidence on the efficacy and safety of ivermectin arising from a study pool that consists mainly of small randomised trials with limited quality in their design, conduct and reporting, does not support using ivermectin for treating or preventing COVID-19 outside of well-designed randomized trials.

John: If you would like to read this review, it's available free online. If you go to Cochrane Library dot com and search 'ivermectin for COVID-19', you'll see the link to the full version.