When the US Food and Drug Administration rejected an antidepressant as a treatment for COVID-19 on Monday, it also released a 27-page memorandum explaining exactly why it wasn’t convinced the drug was effective. It’s an unusual move for the agency, which typically rejects drugs quietly without quite so much publicly available paperwork.

The antidepressant fluvoxamine is a cheap, generic drug that’s been used for decades. Research shows that the drug can also block inflammation in the body. So, some researchers hoped that it could help prevent severe symptoms in patients with COVID-19, some of whom have to cope with inflammation due to overactive immune systems.

Some small and preliminary studies showed that it might be able to reduce the risk of patients with COVID-19 getting seriously sick. But that research wasn’t enough to convince the FDA. The agency said in its memorandum that the studies submitted in support of the drug didn’t do enough to show that it could offer “clinically meaningful outcomes” — reduction in hospitalizations and deaths. The main study, called the Together trial, found that the drug reduced the likelihood a patient would be in the emergency room for longer than six hours. The FDA wasn’t confident that metric was important.

It’s uncommon to get this type of window into the FDA’s decision-making process when it rejects a drug. Most of the time, the decision goes to the pharmaceutical company who made the drug, and it’s kept confidential. Research shows that those companies often don’t announce rejections, and if they do, they don’t say publicly the reason why. People do want to know, though: a survey of adults in the United States published in February found that nearly 90 percent said that they’d want information about why a drug wasn’t approved to be made public.

Notably, the use of fluvoxamine as a COVID-19 treatment wasn’t sent to the FDA by a pharmaceutical company — a group of doctors asked the agency to authorize it. Because it’s an old and generic drug, no pharmaceutical company would profit from taking it through the expensive regulatory process.

One of those doctors, the University of Minnesota infectious disease physician David Boulware, criticized the FDA’s rejection, telling STAT it was “inconsistent.” He noted that the coronavirus antiviral paxlovid is more effective but that it’s not widely available to people in low- and middle-income countries. “It’s not my first choice as a physician but I should have the option,” Boulware said.