The Food and Drug Administration on Monday urged patients and doctors to check that their Ozempic prescriptions are legitimate after the agency seized several hundred units of fake versions of the diabetes drug in the U.S.

Novo Nordisk, the maker of Ozempic and the weight loss drug Wegovy, told the FDA on April 3 that counterfeit 1-milligram injections were being distributed outside its authorized supply chain in the U.S., the agency said in a news release. That means it likely entered the market through unofficial means, like unauthorized distributors or resellers.

The FDA said it seized the counterfeit products — labeled with lot number PAR0362 and serial numbers starting with the first eight digits 51746517 — on April 9.

The agency said it’s aware of six adverse event reports linked to the lot — however, none of them appear to be associated with the counterfeit product. The agency and Novo Nordisk are testing the fake products to identify whether they’re safe. Genuine Ozempic can come with side effects, including stomach problems, so it’s not clear whether the adverse events were caused by typical use.

The fake versions underscore the soaring popularity and demand for the diabetes drug Ozempic, which is often used “off label” for weight loss, as well as similar GLP-1 drugs.

In December 2023, the agency said it seized thousands of units of fake Ozempic and warned that some may still be available for purchase.

The fake products are different from compounded versions of the drug, which have also grown in popularity across the U.S.

The FDA allows compounded versions that are “essentially a copy” of commercially available drugs under special circumstances such as shortages.

In February, the agency said a shortage of Ozempic and Wegovy had been resolved in the U.S., effectively ending the sale of the less expensive compounded versions of the drugs.