US STOCKS-S&P 500, Nasdaq dip with healthcare, Yahoo
* 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. Continuación...