Principle
The Principle trial is studying people aged 50 to 64 who have COVID-19 symptoms and a chronic health condition such as heart disease, asthma or cancer.
It is unclear how many patients are taking part.
It is also open to those aged 65 or over, with or without other illnesses.
The first drug that will be trialled is hydroxychloroquine, sold as Plaquenil. Other potential treatments will be used if they show promise in pre-clinical studies.
The study is being run at the Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) in Surrey.
It will last until March next year.
Recovery
The Randomised Evaluation of COV-id19 thERapY (RECOVERY) trial is being run by the University of Oxford.
It will test the HIV drug lopinavir/ritonavir, marketed as Kaletra and Aluvia, hydroxychloroquine, a malaria medication sold as Plaquenil, and dexamethasone, a type of steroid use in a range of conditions to reduce inflammation.
Almost 1,000 patients from 132 different hospitals have been already recruited in just 15 days.
Thousands more are expected to join the trial in the coming weeks, making it the largest randomised controlled trial of potential COVID-19 treatments in the world.
Definitive results on whether the treatments are safe and effective are expected within months and, if positive, they could potentially benefit hundreds of thousands of people worldwide.
REMAP-CAP
The REMAP-CAP trial is an international effort, with more than 50 research teams around the world taking part.
It is looking specifically at patients who develop community-acquired pneumonia (CAP) as a result of viral infections.
The study will test 16 drugs, including hydroxychloroquine, lopinavir/ritonavir and interferon beta, which have all shown promise in pre-clinical trials.
Between 2,000 and 4,000 patients will be enrolled.