Aspirin does not improve the chances of survival in severely ill COVID-19 patients, early results from one of Britain's biggest trials studying the commonly used painkiller and blood thinner showed on Tuesday.

The scientists behind the trial, which is looking into a range of potential treatments for COVID-19, evaluated aspirin's effects on nearly 15,000 hospitalised patients infected with the novel coronavirus.

Since the drug helps reduce blood clots in other diseases, it was tested in COVID-19 patients who are at a higher risk of clotting issues.

"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," said Peter Horby, co-chief investigator of the trial.

In the study, named RECOVERY, a little less than half of the patients were selected at random and given 150mg of aspirin once a day, and the remaining were given usual care alone.

The trial, run by the University of Oxford, is also looking at the effectiveness of several other treatments, and was the first to show that the widely available steroid dexamethasone, could save lives of people severely ill with COVID-19.

The aspirin study did not show any significant change to the risk of patients progressing to invasive mechanical ventilation. For every 1,000 patients treated with the medicine, about six more patients experienced a major bleeding event and about six fewer experienced a clotting event, Oxford said.

Oxford said the results would be published on online portal medRxiv, and have been submitted for publication at a peer-reviewed medical journal.

RECOVERY also showed anti-inflammatory treatment tocilizumab significantly reduced deaths, but found no benefit for COVID-19 patients from drugs such as antibiotic azithromycin and anti-malarial drug hydroxychloroquine.