The U.S. Department of Justice has launched a civil fraud investigation into UnitedHealth Group, the nation's largest private health insurer, focusing on the company's Medicare billing practices. The investigation, reported by The Wall Street Journal, aims to determine if UnitedHealth inflated medical diagnoses to secure higher payments from federal funds under the Medicare Advantage program. UnitedHealth Group's stock has shed more than $115 billion in value over the past six months, with shares falling 1.5% to $454.94 in midday trading, extending the stock's year-to-date decline to around 10.1%. Sen. Chuck Grassley, chairman of the Senate Judiciary Committee, has also initiated an inquiry into UnitedHealth Group's Medicare billing practices. Grassley has sent a letter to UnitedHealth Group CEO Andrew Witty, requesting detailed information on the company's practices. The news of the investigation led to a 9% drop in UnitedHealth's stock value in a week, marking its worst weekly performance since 2020. UnitedHealth Group has denied the allegations, labeling them as misinformation. The company stated that it consistently performs at the highest levels in government reviews of Medicare Advantage plans. The impact of the news was not limited to UnitedHealth; other insurers operating in the Medicare Advantage market, such as Humana and CVS Health, also saw significant declines in their stock prices, with Humana falling 5.5%, CVS Health dropping 2.3%, and Elevance Health declining 1%. The Department of Justice is also pursuing an antitrust probe against UnitedHealth Group and has filed to block its $3.3 billion acquisition of home healthcare company Amedisys. Additionally, UnitedHealth is under scrutiny by the Federal Trade Commission (FTC) for the role of its subsidiary OptumRx in increasing drug costs.