As western drug companies seek to introduce drugs into the U.S. that were developed in China, the Food and Drug Administration (FDA) is signaling it may not approve.

Food and Drug regulators in the U.S. are wary of some drugs that have been developed in China, specifically regarding the standard of studies looking at medicines there. They’re also worried that U.S. patients haven’t been part of the studies for those medicines.

This could affect the strategies of some drugmakers in the West, like Eli Lilly and Novartis, which were potentially going to make billions of dollars in sales by transferring drugs from China to America. For example, Lilly was hoping to push out a China-developed lung-cancer immunotherapy and offer it at a lower cost than similar medicines already for sale.