The Lancet on Thursday retracted a study that raised safety fears over the use of a drug favored by President Donald Trump to treat Covid-19, after the paper's authors said they could no longer vouch for its underlying data.

It was soon followed by the withdrawal of another coronavirus paper in the New England Journal of Medicine (NEJM) that was not linked to hydroxychloroquine but relied upon the same healthcare company's patient database.

In their paper published on May 22, the authors claimed to have retrospectively analysed some 96,000 patient records, finding that hydroxychloroquine and chloroquine, a related compound, were ineffective against Covid-19 and even increased the risk of death.

This finding led the World Health Organization to temporarily suspend clinical trials into the medicines, though the paper soon triggered widespread concern among scientists over a lack of information about the countries and hospitals that contributed data.

In their retraction statement, the NEJM paper's authors also wrote that the data was not made available to a third-party auditor.