The CBOE Volatility index, the measure of short-term stock market volatility on Wall Street, was last at 20.90 - its highest in a week.
Indexes started higher on Wednesday but then waffled for much of the day before turning sharply lower in the last hour of trading.
Celgene Corp's 9 percent drop (CELG.O) was a drag on the healthcare sector after USA health regulators rejected the company's application seeking approval of a multiple sclerosis drug. It is down 3.9 percent for February but still up 1.5 percent in 2018. The Nasdaq's monthly drop represented its largest since October 2016, and it halted a seven-month rally. The Nasdaq fell 92 points, or 1.3 percent, to 7,180.
USA stocks fluctuated between gains and losses in the morning session on Thursday as Wall Street meditated on a string of economic reports. Gains in the health-care sector which include the volatile marijuana stocks helped lessen downward pressure on the TSX as did strong earnings from Toronto-Dominion Bank.
Drugmaker Celgene sank 8 percent after the FDA said it's not ready to review the company's multiple sclerosis drug.
Energy shares dropped with oil prices and the sector had the biggest daily decline in the S&P 500, but a break below the 50-day moving average on the S&P 500 triggered further selling in afternoon trading.
Wednesday's plunge left the Dow down 6 percent from its January 2018 all-time high, while the S&P 500 is off about 5.5 percent. The Standard & Poor's 500 index erased almost all of its gains for the year.
The S&P 500 slipped less than a point to 2,743.
Having shed 420 points yesterday, the Dow Jones average looked as if it might give a repeat performance today, falling as low as 24,218 at one point before recovering to close at 24,538. The Nasdaq composite was up 10 points, or 0.1 percent, to 7,283. The two-year yield, which moves more on expectations of Fed movements, held steady at 2.22 per cent.
Losses in industrial and health care stocks are pulling major US indexes lower in morning trading on Wall Street.
The gains Wednesday came a day after the indexes fell more than 1 percent on worries about interest rates.
European markets closed mostly lower: London's FTSE 0.1 per cent, Paris closed flat and Frankfurt was 0.3 per cent lower. In Asia, Japan's Nikkei 225 lost 1.6 percent and Hong Kong's Hang Seng rose 0.6 percent.
The S&P 500 ended another turbulent week on an upbeat note Friday, but major indexes posted their worst week of losses since early February as President Donald Trump's threat to impose import tariffs on steel and aluminum rattled investors.