CVS Health CEO Karen Lynch steps down, replaced by David Joyner, after 19% stock plunge

CVS Health said Friday CEO Karen Lynch has stepped down after the pharmacy chain once again warned its earnings will fall short of Wall Street's forecasts. Lynch will be replaced by CVS Caremark president David Joyner, who will attempt to steer the health care giant through a worsening environment of rising medical costs.

CVS, which had cut its financial expectations for the third time in August, said Friday that its third-quarter earnings will fall short of expectations. 

Shares fell $6.27, or 9.9%, to $57.40 in pre-market trading, a decline that comes after the stock had already shed 19% this year.