Six weeks after a controversial meeting with analysts and a mysterious stock price drop, Richard Kogan is retiring as CEO of Schering-Plough(NYSE: SGP).

The trouble started the first week of October, when shares of Schering slipped 15%. Then, late in the evening on Oct. 3, the giant drug maker warned its third-quarter and full-year earnings would be sharply lower than expected.

Furious investors wanted to know why the stock fell in the days leading up to the warning. Did Kogan tell analysts and influential investors beforehand, triggering a selloff? The SEC opened an investigation, presumably to find out if anything said at the meeting was in violation of Regulation Fair Disclosure. The company pledged cooperation and "believes that it has complied with all applicable securities laws in this matter."

The 61-year-old Kogan has been at the helm for six years, and while he undoubtedly had many successes, recent issues have violated investors' trust. Major manufacturing problems, for example, drew regulatory scrutiny and delayed the launch of new drugs.

Interestingly, Dow Jones Newswire says Kogan's departure opens up the possibility that a competitor -- possibly Merck(NYSE: MRK) -- could buy Schering. Stay tuned.