Finished buds sit in a tray at the CannTrust Holdings Inc. cannabis production facility in Fenwick, Ontario, Canada, on Monday, Oct. 15, 2018. Canada, which has allowed medical marijuana for almost two decades, legalizes the drug for recreational use on Oct. 17, joining Uruguay as one of two countries without restrictions on pot and putting the country at the forefront of what could be a $150 billion-plus global market when others follow.

An exchange-traded fund that tracks popular pot stocks fell sharply on Monday, led by shares of Canadian marijuana company Tilray. Traders pointed to profit taking following the legalization of recreational pot in Canada and the end of big conferences earlier in the month.

The ETFMG Alternative Harvest ETF (MJ) dropped more than 9.2 percent, it's second-worst day ever.

Tilray led the sharp decline in pot stocks, falling more than 15.5 percent. Tilray posted its worst day since Oct. 2, when it dropped 16.25 percent. After the bell the company said it issued $25 million in convertible notes in addition to the $450 million in notes tender earlier in the year.

Toronto-listed Aurora Cannabis and Canopy Growth also contributed to the decline, sliding 12.2 percent and 11.2 percent, respectively.