Several authors of a large study that raised safety concerns about malaria drugs for coronavirus patients have retracted the report.

They say independent reviewers weren't able to verify information that’s been widely questioned by other scientists. Thursday’s retraction in the journal Lancet involved a report on hydroxychloroquine and chloroquine, drugs long used for preventing or treating malaria but whose safety and effectiveness for COVID-19 are unknown.

The study linked the drugs to a higher risk of death or heart problems. The study leaders also retracted an earlier report using the same company’s database on blood pressure drugs published by the New England Journal of Medicine.