Pharmaceutical benefit managers (PBMs), a once obscure segment of the health care financing landscape, have become industrial behemoths in the US health sector. In 2017, the top PBMs had revenues that exceeded those of the top pharmaceutical manufacturers, for example, Express Scripts reported revenue of $100 billion while Pfizer had revenues of $52 billion. By one count, “drug channel” companies, which include PBMs and drug distributors, comprise 6 of the top 25 companies on the Fortune list of the top 500 US companies ranked by revenue.