Three of the authors of an influential article that found hydroxychloroquine increased the risk of death in COVID-19 patients have retracted the study, citing concerns about the quality of the data behind it.
The anti-malarial drug has been controversial in part due to support from US President Donald Trump, as well as implications of the study published in British medical journal the Lancet in May.
The three authors said Surgisphere, the company that provided the data, would not transfer the full dataset for an independent review and they "can no longer vouch for the veracity of the primary data sources".
The fourth author of the study, Dr Sapan Desai, the chief executive of Surgisphere, on Thursday declined to comment on the retraction.
The observational study published in the Lancet on 22 May looked at 96,000 hospitalised COVID-19 patients.
It claimed those treated with hydroxychloroquine or the related chloroquine had higher risk of death and heart rhythm problems than patients who were not given the medicines.
Several clinical trials were put on hold after the study was published. The World Health Organization, which paused hydroxychloroquine trials after The Lancet study was released, said on Wednesday it was ready to resume trials.
Many scientists voiced concern about the study. Nearly 150 doctors signed an open letter to the Lancet last week calling the article's conclusions into question.
"I did not do enough to ensure that the data source was appropriate for this use," the study's lead author, Harvard Medical School Professor Mandeep Mehra, said.
"For that, and for all the disruptions - both directly and indirectly - I am truly sorry."
Surgisphere was not immediately available for comment.
"There are many outstanding questions about Surgisphere and the data that were allegedly included in this study," The Lancet said.
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