Pharmaceutical companies are taking advantage of the drug patent system to keep prices of essential medications high, according to a new report — and that includes blockbuster weight-loss drugs and other expensive medications set for government price negotiations this year.

The new findings illustrate how drugmakers file dozens of patents to cover minor modifications in the same drug in order to extend their market exclusivity, delaying the entry of cheaper generic medications and generating billions of dollars in extra revenue.

“We want to expose how the patent system has become a tool to drive the business model and financial gain,” said Tahir Amin, CEO of Initiative for Medicines, Access & Knowledge, a research and policy advocacy organization focused on patent laws that published the report. “It’s a corruption of the patent system.”