Drugmaker Bristol-Myers Squibb has ousted its chief executive Peter Dolan after pressure from federal watchdogs.
A rival firm launched a generic version of Plavix in August
Mr Dolan's departure comes amid an investigation into a failed attempt to delay competition to one of the firm's top drugs - blood thinner Plavix.
Bristol-Myers said his "involuntary departure" stemmed from board worries about a loss of investor confidence.
Analysts expect profits at the group to sink 31% after the recent unexpected launch of a generic form of Plavix.
The company has yet to find a replacement for Mr Dolan, who will stay on as an adviser to help find a new chief.
His departure ends a rocky five year period at the firm - including an accounting scandal and allegations of questionable business deals - which has led to a 60% drop in the value of its shares.
Bristol-Myers' move came a day after a federal monitor, Judge Frederick Lacey, recommended at a board meeting that the company fire both Mr Dolan and the group's chief legal counsel Richard Willard.
Mr Lacey was appointed to investigate the company in June last year after it settled federal charges for an accounting scandal that cost the company $800m.
Under the "deferred prosecution" deal, Bristol-Myers agreed to meet certain standards until 2007 in return for charges against it being dropped.
Mr Lacey and the company refused to comment on the reasons behind the call for Mr Dolan's departure.
However, Bristol-Myers stressed Mr Lacey had not broken any of the terms of the deferred prosecution agreement.
Pressure for Mr Dolan to quit had increased after private firm Apotex launched a generic version of Plavix last month - quickly grabbing a 75% of the market.
The blood-thinning treatment is the second best-selling drug in the world, with annual sales of about $5.9bn.