Veterans advocates say they are frustrated at the lack of transparency around the Department of Veterans Affairs’ use of the unproven drug hydroxychloroquine as a treatment for the coronavirus.

After the release of a preliminary study of veterans hospitalized with COVID-19 last week that showed that hydroxychloroquine — an anti-malaria drug touted by President Donald Trump — had no benefit and caused a greater rate of deaths, the groups want answers and are worried that they may have been misled by the agency on its recent purchase of the drug.

Jeremy Butler, CEO of Iraq and Afghanistan Veterans of America, said that the results of the study were “incredibly troubling for a number of reasons” and that the VA needed to provide answers.

“Why were veterans who were receiving treatment from a federal agency being treated with an unproven and speculative drug?” he asked in a statement. “What was the approval process used by doctors, patients and their families in discussing and agreeing upon this treatment option? At what point did the VA know that the results were this dire and when did they act upon those results? What are the VA’s current procedures for approving and administering the drug?”

The study, which included results from 368 patients, is the largest examination of the drug’s effect on patients suffering from COVID-19, the disease caused by the coronavirus. Researchers concluded that there was a greater prevalence of death among those who took the drug compared to those who received only standard care.

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VA Secretary Robert Wilkie briefly mentioned the study in an interview with MSNBC last week, downplaying its results.

“That’s an observational study,” he said. “It’s not a clinical study. It was done on a small number of veterans — sadly, those of whom were in the last stages of life, and the drug was given to them. And I have to also say that we know the drug has been working on middle-age and younger veterans.”

A VA spokeswoman also pushed back on the idea that the agency was testing the drug on patients even though it has not been scientifically evaluated for its uses to treat COVID-19.

“VA is not testing hydroxychloroquine,” said Christine Noel, the agency’s press secretary. “It is using it to treat COVID-19 in cases where Veteran patients and their providers determine it is medically necessary, and in a manner consistent with current FDA guidance.”

Noel said that the study was not a clinical trial, calling it “an analysis of retrospective data regarding hospitalized patients,” and that the drug was “provided to VA’s sickest COVID-19 patients, many times as a last resort.”

More than 370 veterans have died of the coronavirus, and about 5,800 are confirmed carriers, according to the agency’s numbers Wednesday.

Butler told NBC News that the drug and the study were briefly mentioned in two weekly meetings that veterans service organizations like his have had with agency leaders, including Wilkie.

Multiple attendees of the meetings said they are not open discussions with the organizations. Instead, they said, the VA says how it is handling various challenges, and then leaders take a few questions curated ahead of time.

Butler said the VA first characterized a large purchase of the drug as having been made for its patients who suffer from lupus or arthritis — conditions the drug has been scientifically proven capable of treating. At the most recent meeting Wednesday, leadership briefly touched on the study but quickly moved on, he said.

“In our notes from a week ago, it appeared Wilkie said that they are standing by for medical guidance on hydroxychloroquine,” he said. “We took that as meaning they were not using it.”

Sen. Jon Tester of Montana, the ranking Democrat on the Veteran Affairs Committee, sent questions to the VA about its large order of hydroxychloroquine after the study was released.

“After this order was put in, we asked about the purpose of this order, and we were told it was for routine treatment of lupus and arthritis,” Tester said in his request for information.

Tester also asked whether the patients were being treated after having provided informed consent, what guidance the VA provided to facilities using the drug and whether it was engaged in any further studies.