The Trump administration’s efforts to provide relief from high prescription drug costs aren’t as simple as cutting out the middle man and giving discounts directly to consumers. Some attorneys say it might cause drug companies to reduce discounts to avoid getting snagged by an antitrust law passed during Franklin D. Roosevelt’s administration.

  • No Favoritism: The Robinson-Patman Act was aimed at helping mom-and-pop establishments survive against chain stores by banning sales of the same product to different customers at varying prices....