Many investors are attracted to Pfizer (NYSE:PFE), Merck, and Johnson & Johnson -- the only pharmaceutical companies in the Dow Jones Industrial Average -- for their robust dividends. The cash these companies generate, however, is largely dependent on patent protection for the companies' branded pharmaceutical products. When patents expire, revenue quickly erodes in the face of generic competition.

Pfizer is still dealing with the patent expiration of its megablockbuster drug Lipitor, but are there additional expirations looming in the near future? And how does Pfizer compare with peer Eli Lilly (NYSE:LLY)? In the following video, taken from the Motley Fool's health care show Market Checkup, analysts David Williamson and Max Macaluso discuss these topics in detail.