U.S. Attorney General Jeff Sessions’s decision last week to toss aside federal protections for states opting to liberalize marijuana laws has already caused one company to divert business away from the U.S. and could forfeit a significant global opportunity to countries including Canada.

In a knee-jerk reaction immediately after Sessions rescinded what is known as the Cole Memo, the Canada-based Horizons Marijuana Life Sciences ETF fell as much as 15%. The ETF went on to close down nearly 9%. But the news itself will likely be a boon to the Canadian market.

“You look at the reaction in the market, and there was a selloff in the U.S. and in Canada, which really should be the opposite,” said Nick Kovacevich, chief executive of cannabis packaging company Kush Bottles Inc. KSHB, +1.73% . “The biggest thing that comes to mind for me is Canada. This news is a major blow to our ability to become a global leader, and it just gives Canada more opportunity to capitalize on the market.”

On Friday, the Horizons Marijuana Life Sciences ETF HMMJ, -1.12% gained more than 7%.

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The Canadian government, back in April 2017, introduced long-awaited legislation to federally legalize the sale and production of recreational marijuana by July 2018 — a campaign promise by Prime Minister Justin Trudeau.

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Canada-based medical marijuana company Canopy Growth Corp. WEED, -0.04% said last Friday that it will no longer do business in the U.S., a move that could mark the beginning of company’s leaving the U.S. market to rein in risk. Canopy Growth has a market cap of $6.5 billion, according to FactSet.

“We want to make our position as clear as possible: While Canopy does not support continued cannabis prohibition, it is management’s view that confusion surrounding federal cannabis laws in the United States presents advantages for Canopy Growth, not risks,” Chief Executive Bruce Linton said in a statement. “We are confident in our position because we have exclusively focused on ethical, responsible and legal cannabis opportunities across the globe and not in the United States.”

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Shares of Canopy Growth closed up more than 5% on Friday, a day after Sessions rescinded the Cole Memo. Stocks of a number of marijuana-related stocks based in the U.S., however, continued to suffer.

A number of Australia-based marijuana-related companies saw share gains on Friday after the government announced Thursday that it plans to legalize medical-marijuana exports, a move that is sure to help the country nab a bigger slice of the global market.

“We would like to be, potentially, the world’s No. 1 medicinal cannabis supplier,” Australia’s health minister, Greg Hunt, told reporters.

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Shares of AusCann Group Holdings Ltd. AC8, -6.25% were up more than 26%, while Bod Australia Ltd. shares BDA, -4.68% gained close to 8% and Cann Group Ltd. shares CAN, -1.16% gained nearly 3%.

A November report from cannabis market research firm Brightfield Group projected that the global marijuana market could hit $31 billion by 2021. The report estimated that the current global market is worth roughly $8 billion.

Other estimates suggest the global market could be worth $55 billion by 2025.

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The Brightfield Group report also said the U.S. market is significantly larger than the rest of the world’s, accounting for 90% of global sales, but as Canada adopts legislation to regulate recreational marijuana and other countries soften to medical marijuana, the U.S.’s share is expected to shrink to 57% by 2021.