The Associated Press

UnitedHealth CEO Andrew Witty is stepping down for personal reasons and the nation’s largest health insurer suspended its full-year financial outlook due to higher-than-expected medical costs.

Chairman Stephen Hemsley will become CEO, effective immediately, the Minnesota company said.

Hemsley was UnitedHealth Group CEO from 2006 to 2017. He will remain chairman of the company’s board. Witty will serve as a senior adviser to Hemsley.

It has been a punishing period for UnitedHealth, starting in December when executive Brian Thompson was targeted outside of a New York City hotel and killed. While unrelated to the financial operations of the $340 billion healthcare giant, its shares have tumbled severely since the attack.

Shares of UnitedHealth, which have plummeted 38% since the deadly Dec. 4 ambush of Thompson in midtown Manhattan, fell more than 16% Tuesday to levels last seen almost five years ago.

Other big insurers tumbled as well, with Elevance, Humana and Cigna falling between 4% and 7%.