This article is from the National Bureau of Economic Research. It discusses how pharmaceutical patents prevent generic competitors, but do not protect against market entry of similar products that may be therapeutic competitors. It also discusses how drugs are often created in smaller biochemical firms and given to larger firms to develop because the high start-up costs of Research and Development. This is an example of an natural monopoly.
College bookstores have always held a natural monopoly in the sense that they were the only competitors in the area that provided books to students, forcing students to have to purchase their books at any price. But today in the 21st century, the Internet is bringing in more competition with Amazon, thus driving prices lower for students. Some bookstore CEO praises the new competition.