Investor unrest has brought transition to the top at numerous pharmaceutical companies. In most cases, CEOs are passing the baton after a very successful run, said Michael Kunst, a Munich-based partner with Bain & Company. Their successors will have to navigate increasingly thorny discussions about price and regulation, which is why many companies choose executives from within who already know the business, Kunst said.

"There's a lot mounting up in terms of challenges in an industry that's seen smoother sailing," Kunst said. "These companies are getting into rougher waters, but none are a complete turnaround case that needs new and fresh thinking from outside. The first port of call is definitely internal."