The U.S. Food and Drug Administration has uncovered counterfeit Ozempic shots in the legitimate U.S. drug supply chain, and is warning patients to be on their guard.

The FDA said Thursday that it has seized thousands of counterfeit doses of Ozempic, the weight-loss drug manufactured by Novo Nordisk, but warned that more might still be available for purchase.

Patients, practitioners and pharmacies are specifically warned not to sell or use Ozempic 1-milligram (mg) injections labeled with lot number NAR0074 and serial number 430834149057, the FDA said.

People in possession of Ozempic doses meeting that description can report the counterfeit product directly to the FDA’s Office of Criminal Investigations, the agency said.

The agency and the drugmaker are testing the seized products, but don’t yet have any information yet about the fake drugs’ identity, quality or safety.

Five people have gotten sick from injections of the counterfeit Ozempic, but no cases have been serious, the FDA said.

The sickened patients all suffered side effects consistent with legitimate Ozempic, like nausea, vomiting, diarrhea, abdominal pain and constipation.

The rest of the Ozempic injection package is also counterfeit, including the needles, the injection pen label, the carton and the accompanying doctor and patient information, the FDA said.

Because the needles are counterfeit, their sterility can’t be guaranteed and an injection presents an infection risk to anyone using the fake product, the FDA said. 

In a news release issued Thursday, Novo Nordisk encouraged patients to only buy Ozempic through pharmacies.

“If a prescription is filled via a major retailer who uses our authorized distributors, Novo Nordisk believes the risk of receiving counterfeit product is minimized,” the company said.

The FDA seizures took place in warehouses outside the company’s authorized supply chain, Novo Nordisk told NBC News.