Researchers at the University of Oxford in the U.K. have concluded that hydroxychloroquine does nothing to prevent COVID-19-related deaths.
The research is a continuation of a major clinical trial that found that the drug — which has previously been touted by President Donald Trump and White House trade adviser Peter Navarro — had no clinical benefit.
The study, published in the New England Journal of Medicine, examined the outcomes of 1,561 patients hospitalized with COVID-19 who received hydroxychloroquine and compared them to 3,155 patients who served as a control group.
Within a month, about a quarter of the patients in each group had died.
There was also a slightly higher number of heart-related deaths in the hydroxychloroquine group; however, that finding was not robust enough to be statistically significant — meaning it could have been due to chance.
"The scientific evidence is clear," said Dr. Caleb Alexander, a professor of epidemiology and medicine at the Johns Hopkins Bloomberg School of Public Health. "There is no convincing evidence of its effectiveness for treating COVID."
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Hydroxychloroquine, which has been around for decades, is used to treat malaria and certain autoimmune conditions, including lupus and rheumatoid arthritis.
Its potential for treating COVID-19 first appeared in February with a small study from China. The study did not examine how the drug might work in COVID-19 patients but instead looked at how it behaved on a cellular level in a lab. That is typical of how research on experimental therapies generally begins.
Then, other small studies from China and France hinted that the drug might, indeed, be effective in treating patients. The journal that published the French study, however, later said the article did not meet its expected standard.
Within the next month, Trump publicly began touting the drug as a "game changer." The Food and Drug Administration authorized hydroxychloroquine for emergency use among hospitalized COVID-19 patients, as well as for those in clinical trials.
By April, physicians on the front lines treating seriously ill COVID-19 patients had surmised that hydroxychloroquine did nothing to help. Multiple studies later provided the science to back up what the doctors were saying.
The FDA pulled the emergency use authorization in June. "In light of ongoing serious cardiac adverse events and other serious side effects, the known and potential benefits" of hydroxychloroquine "no longer outweigh those risks," the FDA wrote on its website.
The National Institutes of Health and the World Health Organization also halted COVID-19-related trials of hydroxychloroquine.
This story originally appeared on NBCNews.com.