It’s the latest example of drug hoarding amid a pandemic that has infected over 1 million people in the United States and threatened to expose many more. Like hydroxychloroquine, which was in short supply after being touted by President Trump during White House briefings as a potential “game-changer” coronavirus treatment, famotidine has proven uses and patients who need the drug for those purposes. But because it is being tested by researchers, people are preemptively stocking up — even though experts advise that the drug is unproven as a coronavirus treatment.

The clinical trial using the drug, which was first reported by the magazine Science, began April 7 and has been largely under wraps to ensure that the drug was in supply for other uses.

“If we talked about this to the wrong people or too soon, the drug supply would be gone,” Kevin Tracey, a former neurosurgeon in charge of the Northwell hospital system’s research, told Science.

Researchers are administering nine times the amount of famotidine intravenously that someone would usually take to treat heartburn to at least 187 coronavirus patients in critical status. Northwell Health CEO Michael Dowling told CNBC on Tuesday that he expects in “the next two weeks or so” that there will be “potential results to be able to tell whether it’s working or not.”

Since the news of the study, online retailers were largely sold out Monday and Tuesday, and Walgreens and CVS reported shortages.

“We’re closely monitoring the situation, and continue to work with our supplier partners to best meet the needs of our patients,” Walgreens spokeswoman Emily Hartwig-Mekstan said in an email.

Mike DeAngelis, a spokesman for CVS, said the pandemic had deepened an existing dearth of the drug after a recent recall of Zantac and other ranitidine products had also depleted the supply.

The Food and Drug Administration was already wary of a shortage of the critical ingredients in most drugs, which are overwhelmingly made in China, where the virus originated. After there was a shortage of two anti-malarial drugs touted by Trump, without definitive evidence that the drugs were effective or approval from the Food and Drug Administration, experts worry about a shortage of the heartburn medicine, which is more accessible because it’s sold over the counter.

The hydroxychloroquine shortage threatened lupus and rheumatoid arthritis patients who depend on those drugs to alleviate symptoms of inflammation, including preventing organ damage in lupus patients, David Margraf, pharmaceutical research scientist and member of the Resilient Drug Supply Project team at the Center for Infectious Disease Research and Policy, told The Post.

“Anytime there’s a purported treatment, especially since it’s over the counter, people are going to grab it,” Margraf said.

He said pandemic-caused shortages come on top of already critical concerns. His team found that about 60 of 156 drugs used in acute care — which, if unavailable for a few hours or days, can lead to increased fatalities — were affected by shortages before the emergence of the virus.

While the drug’s use for heartburn isn’t critical, the over-the-counter medicine has other purposes. Famotidine can be used in emergency rooms as part of a treatment regimen for allergic reactions or in intensive care units for stress ulcer prevention, Bryan D. Hayes, a pharmacist for Massachusetts General Hospital’s Department of Emergency Medicine and a Harvard University assistant professor, told The Post.