Danish drugmaker Novo Nordisk said on Monday several hundred counterfeit units of its diabetes drug Ozempic were being distributed outside its authorized supply chain in the United States.

The country's health regulator seized the counterfeit injections on April 9 and is investigating them.

Surging demand for Novo's Ozempic, chemically known as semaglutide, has given rise to concerns about unregulated, compounded and counterfeit medicines. Its weight-loss drug Wegovy also has the same active ingredient.

As the investigation continues, further analyzes, including extensive visual examination and chemical testing of the seized, counterfeit product is underway. The U.S. Food and Drug Administration and Novo Nordisk do not yet have information about the drugs' identity, quality, or safety, the regulator said on its website.

Novo has advised retail pharmacies to purchase authentic Ozempic injections from authorized distributors and urged patients to check their product for any signs of counterfeiting before using.