* TSX ends down 262.71 points, or 1.90 percent, at 13,529.17
* All of the TSX's 10 main groups fall (Adds strategist comment, updates prices to close)
By John Tilak and Alastair Sharp
TORONTO, Oct 30 (Reuters) - Canada's main stock index fell sharply on Friday, pushed lower by a slump in Valeant Pharmaceuticals International Inc after it cut ties with a specialty pharmacy accused of helping it inflate revenue, and by retreats in heavyweight banks.
The most influential single weight on the index was Valeant, which fell 17.7 percent after it said it will sever ties with Philidor Rx Services in the wake of criticism over the relationship between the two closely associated companies.
The Toronto Stock Exchange's S&P/TSX composite index closed down 262.71 points, or 1.90 percent, at 13,529.17. All 10 of its main groups fell. It lost 3 percent on the week but gained 1.7 percent through October.
"Much of the action has been caused by the collapse of Valeant," said Elvis Picardo, strategist and vice president of research at Global Securities in Vancouver.
"The weakness in crude oil hasn't helped as well," he said.
The overall energy group retreated 0.4 percent, with Husky Energy Inc down 12.8 percent to C$17.67 after swinging to a quarterly loss on a writedown and impairment charge.
U.S. crude prices recovered from early losses to rise 0.8 percent to $46.42 a barrel.
Barrick Gold fell 2.5 percent to C$10.05. The world's biggest gold producer said on Thursday it will increase its focus on productivity gains in 2016.
The materials group, which includes miners, fell 1.6 percent, with fertilizer company Potash Corp down 3.1 percent at C$26.48, a day after cutting its output and earnings forecast.
Financials retreated 1.9 percent, with Royal Bank of Canada down 2.2 percent to C$74.77. (Reporting by Alastair Sharp; Editing by Dan Grebler and James Dalgleish)