A major British clinical trial found that hydroxychloroquine has “no benefit” to patients hospitalized with COVID-19, scientists said Friday in the first large-scale study at the center of political and scientific controversy to provide results for a drug.

Hydroxychloroquine, a decades-old medicine for malaria and rheumatoid arthritis, has been hailed by high-profile figures, including US President Donald Trump, as a possible treatment for the new coronavirus, and has been included in several randomized clinical trials.

Recovery study at the University of Oxford, the largest of these to come up with results, said it will now avoid recruiting patients for hydroxychloroquine “with immediate effect.”

“Our conclusion is that this treatment does not reduce the risk of dying from COVID among hospital patients and that clearly has a significant importance for the way patients are treated, not only in the UK, but all around the world,” said Martin Landray, an Oxford professor of medicine and epidemiology who co-leads the study.

The randomized clinical trial — considered the clinical research gold standard — has enrolled a total of 11,000 patients from 175 hospitals in the UK to test a variety of new therapies.

Certain medications that are still being studied include: the combination of HIV antivirals Lopinavir and Ritonavir; a low dose of Dexamethasone steroid, usually used to minimize inflammation; Azithromycin antibiotic; and Tocilizumab anti-inflammatory medication.

Researchers are now studying convalescent plasma from the blood of people recovering from COVID-19, which includes antibodies to counter the virus.

They said 1,542 patients were randomly assigned to hydroxychloroquine, compared with 3,132 standard hospital-only patients.

After 28 days between the two groups they found “no substantial difference” in mortality, and no evidence that opioid treatment shortens the amount of time spent in hospital.

“This is a really important result, at last providing unequivocal evidence that hydroxychloroquine is of no value in the treatment of patients hospitalized with COVID-19,” said Peter Openshaw, a professor at Imperial College London, in reaction to the results.

He noted that the medication was “very dangerous” and patients would profit from suspending the trials.

Hydroxychloroquine has been in use for years but it has many potentially dangerous side effects, including heart arrhythmia.