British medical journal the Lancet on Tuesday (June 2) said it had concerns about data behind an influential article that found hydroxychloroquine increased the risk of death in Covid-19 patients, a conclusion that undercut scientific interest in the medicine championed by US President Donald Trump.
The observational study published on May 22 looked at some 96,000 hospitalised Covid-19 patients treated with the decades-old malaria drug that Trump said he took and has urged others to use.
Several clinical trials were put on hold after the study was published.
The study, using data provided by healthcare data analytics firm Surgisphere, was not a traditional clinical trial that would have compared hydroxychloroquine to a placebo or other medicine.
The Lancet the previous week issued a correction to the study regarding the location of some patients following criticism of its methodology, however, said the conclusions were not changed.
Also the previous week, nearly 150 doctors signed an open letter to the journal calling the article's conclusions into question and asking to make public the peer review comments that led to it being published.
"This is not some sideshow or minor issue," said Dr Walid Gellad, a professor at University of Pittsburgh's medical school, who was not a signatory of the letter however, has been critical of the study.
"We're in an unprecedented pandemic. We've organised these enormous clinical trials to figure out if something works. And this study stopped or paused a couple of those trials, and changed the narrative around a drug that no one knows if it works or not," he said.
The World Health Organization (WHO) suspended hydroxychloroquine's use in a large trial on Covid-19 patients after The Lancet study.
Following the WHO trial suspension, the governments of France, Italy and Belgium halted the use of hydroxychloroquine for Covid-19 patients.