Shares of UnitedHealth Group ended down 22% Thursday after the health-care giant's first-quarter results fell short of analysts' estimates and it cut its profit forecasts for 2025.

A surprising Medicare Advantage cost spike helped push UnitedHealth into a rare deep dive Thursday, after the health care giant chopped its 2025 forecast following a worse-than-expected first quarter.

UnitedHealth Group surprised investors with what its CEO said was an "unusual and unacceptable" quarterly earnings miss, and it lowered its outlook for the full year due to higher-than-expected medical costs,