Seriously sick coronavirus patients in New York state’s largest hospital system are being given massive doses of vitamin C — based on promising reports that it’s helped people in hard-hit China, The Post has learned.

Dr. Andrew G. Weber, a pulmonologist and critical-care specialist affiliated with two Northwell Health facilities on Long Island, said his intensive-care patients with the coronavirus immediately receive 1,500 milligrams of intravenous vitamin C.

Identical amounts of the powerful antioxidant are then readministered three or four times a day, he said.

Each dose is more than 16 times the National Institutes of Health’s daily recommended dietary allowance of vitamin C, which is just 90 milligrams for adult men and 75 milligrams for adult women.

The regimen is based on experimental treatments administered to people with the coronavirus in Shanghai, China, Weber said.

“The patients who received vitamin C did significantly better than those who did not get vitamin C,” he said.

“It helps a tremendous amount, but it is not highlighted because it’s not a sexy drug.”

A spokesman for Northwell — which operates 23 hospitals, including Lenox Hill Hospital on Manhattan’s Upper East Side — said vitamin C was being “widely used” as a coronavirus treatment throughout the system, but noted that medication protocols varied from patient to patient.

“As the clinician decides,” spokesman Jason Molinet said.

About 700 patients are being treated for coronavirus across the hospital network, Molinet said, but it’s unclear how many are getting the vitamin C treatment.

The vitamin C is administered in addition to such medicines as the anti-malaria drug hydroxychloroquine, the antibiotic azithromycin, various biologics and blood thinners, Weber said.

As of Tuesday, New York hospitals have federal permission to give a cocktail of hydroxychloroquine and azithromycin to desperately ill patients on a “compassionate care” basis.

President Trump has tweeted that the unproven combination therapy has “a real chance to be one of the biggest game changers in the history of medicine.”

Weber, 34, said vitamin C levels in coronavirus patients drop dramatically when they suffer sepsis, an inflammatory response that occurs when their bodies overreact to the infection.

“It makes all the sense in the world to try and maintain this level of vitamin C,” he said.

A clinical trial on the effectiveness of intravenous vitamin C on coronavirus patients began Feb. 14 at Zhongnan Hospital in Wuhan, China, the epicenter of the pandemic.

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The randomized, triple-blind study will involve an estimated 140 participants and is expected to be complete by Sept. 30, according to information posted on the US National Library of Medicine’s website.