* TSX falls 16.81 points, or 0.11 percent, to 14,635.64
* Seven of the TSX's 10 main groups move lower
TORONTO, Nov 8 (Reuters) - Canada's main stock index slipped on Tuesday as a fall in oil prices weighed on energy stocks and investors braced for the outcome of one of the most contentious U.S. presidential elections in history.
Meanwhile, Valeant Pharmaceuticals International Inc slumped 20.2 percent to C$20.37 after the drugmaker cut guidance for the year and warned that 2017 could be even more challenging as some products face new competition.
At 10:21 a.m. EDT (1521 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 16.81 points, or 0.11 percent, at 14,635.64. Seven of the index's 10 main groups were in negative territory.
The index posted its biggest gain in nearly three weeks on Monday, helped after the FBI announced on Sunday that it had not changed its conclusion that Democratic nominee Hillary Clinton should not be charged over her use of a private email server.
Clinton, seen by investors as offering greater certainty and stability, has a 90 percent chance of defeating Republican nominee Donald Trump, according to the final Reuters/Ipsos States of the Nation poll released on Monday.
On Tuesday, the energy group retreated 0.6 percent as oil prices eased, with Canadian Natural Resources Ltd falling 0.9 percent to C$40.26 and Suncor Energy Inc shedding 0.5 percent to C$39.90.
Industrials fell 0.4 percent, with Canadian Pacific Railway Ltd down 1.4 percent to C$189.14 and Canadian National Railway Co declining 0.8 percent to C$84.23.
The financials group slipped 0.2 percent.
The materials group, which includes precious and base metals miners and fertilizer companies, bucked the broader trend by rising 1.4 percent.
Gold futures were up 0.4 percent to $1,283.5 an ounce, while copper prices advanced 2.6 percent to $5,230 a tonne.
U.S. crude prices were down 0.7 percent to $44.59 a barrel, while Brent lost 0.7 percent to $45.81.
The value of Canadian building permits fell by the most in eight months in September, driven by a decline in construction intentions for commercial buildings, though residential plans rose, data from Statistics Canada showed on Tuesday. (Reporting by Alastair Sharp; Editing by Paul Simao)