(CNN) Coronavirus patients taking hydroxychloroquine, a treatment touted by President Trump, were no less likely to need mechanical ventilation and had higher deaths rates compared to those who did not take the drug, according to a study of hundreds of patients at US Veterans Health Administration medical centers.

The study, which reviewed veterans' medical charts, was posted Tuesday on medrxiv.org , a pre-print server, meaning it was not peer reviewed or published in a medical journal. The research was funded by the National Institutes of Health and the University of Virginia.

In the study of 368 patients, 97 patients who took hydroxychloroquine had a 27.8% death rate. The 158 patients who did not take the drug had an 11.4% death rate.

"An association of increased overall mortality was identified in patients treated with hydroxychloroquine alone. These findings highlight the importance of awaiting the results of ongoing prospective, randomized, controlled studies before widespread adoption of these drugs," wrote the authors, who work at the Columbia VA Health Care System in South Carolina, the University of South Carolina and the University of Virginia.

Researchers also looked at whether taking hydroxychloroquine or a combination of hydroxychloroquine and the antibiotic azithromycin, had an effect on whether a patient needed to go on a ventilator.

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