Key Takeaways

Major U.S. equities indexes were mixed on the final day of an abbreviated trading week, with markets set to remain closed on Good Friday.

The S&P 500 ended Thursday's session with a minor gain of 0.1%. The Dow slid 1.3%, dragged down by a steep decline for health insurance constituent UnitedHealth Group ( UNH ). After fluctuating for much of the day, the Nasdaq closed 0.1% lower.

Eli Lilly ( LLY ) shares notched the S&P 500's top daily performance, surging 14.4% after the pharmaceutical giant released promising results from a clinical trial of its experimental oral weight-loss treatment. According to Lilly, the first in a series of Phase 3 trials revealed that orforglipron was more effective than a placebo at causing weight loss and reducing A1C, a long-term gauge of blood sugar levels. The company expects to seek Food and Drug Administration (FDA) approval next year for orforglipron as a type 2 diabetes treatment.

Dollar Tree ( DLTR ) shares added 8.1% on Thursday. The stock trended higher in April, and analysts suggested that the discount retailer could be poised for strength amid the challenging macroeconomic backdrop. For instance, Citi upgraded Dollar Tree stock last week , suggesting that the company could emerge as an unlikely beneficiary of broadly applied tariffs, with flexibility to raise prices without deterring too many customers and a track record of success during previous downturns.

Crude oil futures prices pushed higher for the second straight day after the U.S. announced additional sanctions targeting Iran's oil business. The uptick in oil prices helped lift a variety of oil and gas stocks. Shares of exploration and production firm Diamondback Energy ( FANG ) gained 5.7%, while shares of oilfield services provider Halliburton ( HAL ) advanced 5.1%.

Shares of UnitedHealth plummeted 22.4% after the insurance giant reported lower-than-expected sales and profits for the first quarter. It was the heaviest decline in the Dow and the S&P 500. The company also reduced its full-year profit guidance . Other health insurance stocks also lost ground, with shares of Humana ( HUM ) falling 7.4%.