Aspirin has been added to a British trial of possible treatments for Covid-19.
The painkiller will be assessed to see whether it might reduce the risk of blood clots in people with the disease.
The trial is taking place at 176 hospitals across the UK, and has so far recruited more than 16,000 patients.
The scientists behind the Recovery trial, which is looking into a range of potential treatments for Covid-19, said it would include the drug, which is commonly used as a blood thinner.
"There is a clear rationale for believing that it (aspirin) might be beneficial, and it is safe, inexpensive and widely available," said Peter Horby, co-chief investigator of the trial, which according to the Recovery website is the world's largest.
"We are looking for medicines for Covid-19 that can be used immediately by anyone, anywhere in the world. We do not know if aspirin is such a medicine but we will find out."
Patients infected with the coronavirus are at a higher risk of blood clots because of hyper-reactive platelets, the cell fragments that help stop bleeding. Aspirin is an antiplatelet agent and can reduce the risk of clots, the Recovery trial's website said.
At least 2,000 patients are expected to randomly get 150mg of aspirin daily, along with the usual regimen. Data from those patients will be compared with at least 2,000 other patients who receive the standard coronavirus treatment on its own, the website showed.
Small daily doses of aspirin has been found to reduce the risk of certain cancers. As a blood thinner, it increases the risk of internal bleeding, and taking too much over a long period of time has been associated with kidney damage.
Other treatments being tested in the Recovery trial include common antibiotic azithromycin and Regeneron's antibody cocktail that was used to treat US President Donald Trump's Covid-19 symptoms.
Unlike Gilead's remdesivir, which has been approved as a Covid-19 treatment in the US but has shown poor results in a major World Health Organisation trial, aspirin is a generic drug, making it much cheaper.
The Recovery trial was the first to show that dexamethasone, a steroid which is also cheap and widely available, could save lives of people severely ill with Covid-19.
It also showed that the anti-malarial drug hydroxychloroquine, once touted by Mr Trump, was of no benefit in treating Covid-19 patients.
Prof Martin Landray from the Nuffield Department of Population Health, who co-leads the Recovery trial, said: "Aspirin is widely used to prevent blood clots in many other conditions, including heart attack, stroke, and pre-eclampsia in pregnant women. But enrolling patients in a randomised trial such as Recovery is the only way to assess whether there are clear benefits for patients with Covid-19 and whether those benefits outweigh any potential side effects, such as the risk of bleeding."
The decision to add aspirin to the scheme was made by University of Oxford researchers leading the trial in conjunction with the Chief Medical Officer, following a recommendation by the UK Covid-19 Therapeutics Advisory Panel.
