The U.S. Federal Trade Commission and the Department of Justice have floated a new set of guidelines that would govern their reviews of mergers in a variety of markets, including the drug and device industries. While many of these guidelines are vaguely worded and open to interpretation, one of the more ambiguously worded passages states that a merger may be rejected if it could create “a clog on competition,” a phrase that appears in a Supreme Court decision handed down more than 60 years ago.