U.S. President Donald Trump said on Thursday that the price of Novo Nordisk's best-selling weight-loss drug would be lowered and that negotiations over price changes would be swift.

Novo-Nordisk A/S fell 3% and Eli Lilly fell 4% in aftermarket trading on Thursday.

Trump made the comments during a White House event on fertility treatments and drug pricing. He was asked by reporters to identify the name of a drug that he earlier in the event said would be made less expensive.

"I was referring to Ozempic, or - I was referring to - the fat loss drug?.... They'll be much lower," Trump said.

Novo sells Ozempic for managing diabetes while Wegovy is approved for weight-loss. Both drugs contain the same active ingredient, semaglutide.

Asked for comment, a Novo spokesperson said: "Novo Nordisk has engaged in discussions with the Administration regarding the Most Favored Nation executive order." The spokesperson said the company was focused on improving patient access and affordability, but did not comment directly on Trump's remarks.

Trump earlier said that under his administration's plans, the price of the drug would be reduced to $150 from $1,300. Ozempic has a list price of about $1,000 for a month's supply but is sold directly by Novo to cash-pay customers for $499 per month.

During the same White House event, Dr. Mehmet Oz, who runs the Centers for Medicare and Medicaid Services, said that the agency had not yet finished negotiating the price for GLP-1 drugs, which are used to treat diabetes and obesity.

Novo's Ozempic is one of the drugs that the agency has chosen for price negotiations.