What happened Shares of Amarin (NASDAQ: AMRN) were 10.4% lower as of 11:20 a.m. EDT on Tuesday. The decline came after the drugmaker announced that John Thero plans to retire as president and CEO effective Aug. 1. So what It's not unusual for changes at the CEO level to cause a biotech stock to fall, especially when the CEO's departure is unexpected. But in this case, there don't appear to be any yellow flags with Thero stepping down. Image source: Getty Images. Thero was CEO for the last seven years and he's now 60, an age when many people retire. Amarin has already named his successor: Karim Mikhail, senior vice president and head of commercial for Europe, will take the reins in August. Perhaps the main reason for Amarin's shares sinking today is that Thero's exit could lower the prospects of any merger and acquisition deals over the near term. Amarin is viewed by some as a potential buyout target. Now what The main things to watch with Amarin are the company's launch of Vascepa in Europe and the anticipated approval of the drug in China later this year. Mikhail's track record of more than 20 years at Merck, including leading the big drugmaker's commercial operations for its lipid drugs, seems to make him a good fit to take the baton from Thero in overseeing these efforts. 10 stocks we like better than AmarinWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Amarin wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of February 24, 2021 Keith Speights has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.Source