* Valeant sinks after Citron report, drags Allergan, Endo
* GM, Boeing rise after strong results
* Ferrari up on debut
* Dow flat, S&P down 0.3 pct, Nasdaq down 0.6 pct (Updates to late afternoon)
By Abhiram Nandakumar
Oct 21 (Reuters) - The S&P 500 and Nasdaq slipped in choppy trading late Wednesday afternoon as insurers and other big healthcare names dropped and Yahoo shares fell following disappointing results.
Valeant Pharmaceutical's U.S.-listed shares dropped sharply, hitting a low of $88.50, after short-seller Citron Research released a report critical about the company.
The stock later pared losses and was last at $120.39 after investor Bill Ackman said he increased his Valeant stake on Wednesday by 2 million shares, according to CNBC.
Shares of Allergan, which has a business model similar to that of Valeant, fell 4.6 percent to $251.37, though the company said nearly all of its drugs are being distributed through traditional wholesale and retail channels. Endo International fell 7.7 percent to $58.05.
Health insurers Aetna, Humana, Anthem and Cigna slipped after Democratic presidential candidate Hillary Clinton said she had "serious concerns" about the mergers the companies were proposing.
On the plus side, shares of General Motors rose 6.5 percent to $35.64, while Boeing rose 1.7 percent to $141.31, after both industry heavyweights reported better-than-expected results.
Yahoo was down 4.9 percent at $31.22, a day after the Internet company's quarterly earnings and profit missed expectations.
"Earnings are a mixed bag but you've seen the market rally over the last six years without strong earnings," said Adam Sarhan, chief executive of Sarhan Capital in New York.
The outlook for interest rates remains a bigger factor right now for the market, he said, adding "the easy money trading trumps everything else."
Stocks have mostly gained this month following a sharp selloff in the third quarter. The Federal Reserve decided against raising rates at is September meeting.
At 3:20 p.m., the Dow Jones industrial average was unchanged at 17,217.11, the S&P 500 lost 6.72 points, or 0.33 percent, to 2,024.05 and the Nasdaq Composite dropped 27.01 points, or 0.55 percent, to 4,853.96.
Of the S&P 500 companies that have reported results so far, 42 percent have exceeded revenue estimates, though about 60 percent typically beat estimates in a quarter, according to Thomson Reuters data.
Ferrari was up 8.5 percent at $56.42 in its debut on the New York Stock Exchange.
Declining issues outnumbered advancing ones on the NYSE by 1,984 to 1,053, for a 1.88-to-1 ratio on the downside; on the Nasdaq, 1,899 issues fell and 846 advanced for a 2.24-to-1 ratio favoring decliners.
The S&P 500 posted 27 new 52-week highs and 5 new lows; the Nasdaq recorded 52 new highs and 79 new lows. (Additional reporting by Abhiram Nandakumar in Bengaluru; Editing by Don Sebastian and Chizu Nomiyama)