There was a rule passed during Trump's first term, that they couldn't charge you more than the actual cost for generic drugs.

Example: The real price of the drugs is $10, but your copayment is $30. They would charge you $30 and pocket the profit of $20. They changed the rule so that they're only allowed to charge you $10 in this example. For generic drugs, the actual cost will frequently be less than the copayment.