Long-term CVS Health Chief Executive David Joyner has replaced Karen Lynch as CEO as the company struggles to deliver higher profits and stock performance, CVS announced Friday.

The move takes effect Thursday, the day before the announcement, as CVS shares have fallen nearly 20% this year. Shares fell about 13% in premarket trading on Friday.

CVS has faced challenges as higher medical costs weigh on its Aetna insurance unit and consumer spending declines at its retail pharmacies. In August, the company cut its full-year profit forecast and said it would cut costs by $2 billion over the next few years.

In its press release Friday, CVS also said it expected third-quarter adjusted earnings to be between $1.05 and $1.10 per share. It expects medical costs to be higher than previously expected, with a so-called medical benefit ratio of 95.2% in the quarter.

“Given continued elevated medical cost pressures in the Health Care Benefits segment, investors should no longer rely on the Company's prior guidance provided in its second quarter 2024 earnings conference call on August 7, 2024,” CVS said in the Press release.

The company is expected to report its third-quarter results on November 6.

Last month, major CVS shareholder Glenview Capital launched a significant push for changes at the company, CNBC previously reported.

CNBC reported last month that CVS's board had hired strategic advisers to weigh its options, including the possibility of dissolving its insurance and retail businesses.

Joyner most recently led the company's pharmacy services business as president of CVS Caremark, a position similar to Lynch, before taking the top job in February 2021. He began his career at Aetna in pharmacy benefit services and previously held the role of executive vice president of sales and marketing at CVS Health.

“We believe David and his deep understanding of our integrated business can help us more directly address the challenges facing our industry, accelerate the operational improvements our business requires, and fully realize the value we can uniquely create,” CEO Roger Farah said in a statement.

Lynch also resigned from the company's board this week, the company said Friday. Joyner will take a seat on the board and Farah will assume the role of chairman.

—CNBC's Annika Kim Constantino and Rohan Goswami contributed to this report.