President Donald Trump has been threatening tariffs on pharmaceuticals for months. This week, he told CNBC that he’s planning to impose a “small tariff” on prescription drugs soon and then raise that to 250% over the next year or year and a half.

An estimated 90% of prescriptions filled in the U.S. every year are generics. That includes most pills you’d get at the pharmacy, like blood pressure drugs and statins, according to John Murphy, president and CEO of the Association for Accessible Medicines.

“We manufacture about 45% of the pill needs for patients in the United States. And the rest of that is, of course, imported,” he said, from places like India, Europe, and China. “So it's a pretty global supply chain.”

That’s also true for injectable medications you might get at the hospital, like IV fluids and many cancer drugs.

It’s a different story with more expensive brand-name drugs, said Marta Wosińska, a senior fellow at the Center on Health Policy at Brookings.

“The manufacturers that make branded products tend to have facilities on both sides of the pond,” she said.

It would be easier for those companies to move more production to the U.S if necessary than it would be for makers of cheaper generics, she added.

Mariana Socal, an associate professor at the Johns Hopkins School of Public Health, said that it would also be easier for makers of brand-name drugs to absorb tariffs.

“But for generic drugs, you know, they are not patented — very cheap drugs. The markup for the drug manufacturer is not that high, and manufacturers are already squeezed in their profits for these drugs,” she said.

So, with tariffs, they could start losing money, noted Marta Wosińska at Brookings.

“The cost that I worry about,” she said, “is not that prices for generics might increase, it’s that manufacturers just might throw their hands up and say, ‘You know, I don't want to sell in the U.S. market.’”

And that could mean that drug shortages become more common.