Marijuana companies were among the most heavily traded stocks on the index.
At 10:12 AM ET (15:12 GMT), the Toronto Stock Exchange's S&P/TSX composite index fell 77.19 points, or 0.49 percent, to 15,528.84. The index was trading at its lowest level since September.
The TSX posted no new 52-week highs and 27 new lows. Across all Canadian issues there were 4 new 52-week highs and 93 new lows.
The largest percentage gainer on the TSX was Canopy Growth Co, which rose 6.8 percent, while the largest decliner was Prometic Lfe Scn, down 5.9 percent.
Among the most active Canadian stocks by volume were Aurora Cannabis, up 7.3 percent to $9.12; Aphria Inc , up 5.0 percent to $14.58 and Canopy Growth Co , up 6.8 percent to $25.75.
Among industrial stocks, Bombardier Inc slipped 1.7 percent to C$3.23.
In the financial sector, Toronto Dominion Bank lost 1.3 percent to C$72.97, and Canadian Imperial Bank of Commerce gave back 1.4 percent to C$117.58.