The cheap and widely-available drug aspirin does not improve survival for patients hospitalized with Covid-19, a U.K. study has found.

Oxford University researchers had hoped to find that the blood-thinning medicine could help hospitalized Covid-19 patients who are at an increased risk of clots forming in their blood vessels, particularly in the lungs, but found aspirin didn’t help to prevent deaths.

The study — part of a wider “RECOVERY” trial investigating various possible treatments for people hospitalized with coronavirus — involved nearly 15,000 patients hospitalized with the virus. Roughly half of the patients were given 150mg of aspirin daily compared to the other half which were given the usual care alone.

The study found that “there was no evidence that aspirin treatment reduced mortality” and “no significant difference” in the number of people that died, with 17% of people in both groups dying in hospital after 28 days.

“The data show that in patients hospitalised with Covid-19, aspirin was not associated with reductions in 28-day mortality or in the risk of progressing to invasive mechanical ventilation or death,” Peter Horby, professor of emerging infectious diseases in the Nuffield Department of Medicine at the University of Oxford, and joint chief investigator for the RECOVERY trial, said of the study.

“Although aspirin was associated with a small increase in the likelihood of being discharged alive this does not seem to be sufficient to justify its widespread use for patients hospitalised with Covid-19.”

Martin Landray, a professor of medicine and epidemiology at the Nuffield Department of Population Health at the University of Oxford and one of the chief investigators in the study, described the results as “disappointing.”

“There has been a strong suggestion that blood clotting may be responsible for deteriorating lung function and death in patients with severe Covid-19. Aspirin is inexpensive and widely used in other diseases to reduce the risk of blood clots so it is disappointing that it did not have a major impact for these patients. This is why large randomised trials are so important – to establish which treatments work and which do not.”

The RECOVERY trial has already made several life-saving discoveries, one being that dexamethasone, a cheap and widely used steroid, was able to save lives among severely ill Covid-19 patients.

The results of the latest aspirin study will be published shortly on pre-print site medRxiv and have been submitted to a leading peer-reviewed medical journal.