Herbalife fell a second session after widely-followed hedge fund manager Bill Ackman outlined his case for shorting the nutrition and skin-care products company. Ackman criticized Herbalife, saying the company is a "pyramid scheme" that has grown rapidly without demonstrating "much substance" to justify the growth. The company has shed more than 20 percent in the last two days. (Read More: Herbalife Disputes Ackman's Claim of 'Pyramid Scheme')
Merck slumped after the pharmaceutical company said its cholesterol drug study failed. The company said it no longer plans to seek approval for the drug in the U.S.
NYSE Euronext skyrocketed to lead the S&P 500 gainers after IntercontinentalExchange agreed to acquire the financial services company in a deal worth nearly $8.2 billion. The offer values NYSE shares at $33.12, a 38 percent premium over Wednesday's closing price. The acquisition is expected to close in the second half of 2013.
Among earnings, Rite Aid surged after the drugstore chain posted its first quarterly profit in more than five years and boosted its forecast for the year.
ConAgra Foods edged higher after the packaged foods company posted better-than-expected earnings, and said its full-year profit will be at the high end of estimates.
Among earnings, Nike and Research In Motion are among notable companies slated to report after the closing bell.
Also on the economic front, weekly jobless claims climbed 17,000 to a seasonally adjusted 361,000 in the previous week, according to the Labor Department. The four-week moving average for new claims, fell 13,750 to 367,750, the lowest since late October. And leading indicators slipped 0.2 percent to 95.8 in November, according to the Conference Board.