This article was updated on 1 May and again on 6 July. Since its original publication on 17 April, the number of COVID-19 clinical trials has increased from 524 to 2,378. There is no cure for COVID-19. Researchers are testing existing drugs to see if they act against SARS-CoV-2 or alleviate the symptoms of the disease. New drugs are also in development, but this is at a very early stage. Results from trials on existing drugs have already been reported with some positive findings. Dexamethasone is a cheap steroid drug that reduces the risk of death of ventilated patients by 35% and by 20% for patients requiring oxygen therapy. Remdesivir is an antiviral drug; there is good evidence that it can reduce the length of time that hospitalised COVID-19 patients are ill. Negative findings are valuable because they allow researchers to focus on other drugs; there is good evidence that hydroxychloroquine does not offer any benefits to treat COVID-19 patients. Research to see if it might have a protective effect for at-risk groups, such as healthcare workers, is ongoing. There are numerous trials in progress to test a range of drugs that act on the immune system.