STOCKHOLM—A Swedish January is dark, cold and snowy, but in Stockholm cannabis stocks were lighting up the screens of investors.

“Out of nowhere, the interest for Canadian cannabis shares has completely exploded in Sweden,” said Joakim Bornold, a savings adviser at online broker bank Nordnet AB.

Two Canadian cannabis companies, Aurora Cannabis Inc. and Canopy Growth Corp., were among the top 10 most traded shares on Nordnet in January, he said. That list usually consists of companies such as Investor AB, Hennes & Mauritz AB, Nordea Bank AB and Ericsson AB.

The green-leafed intoxicant is the latest fad to catch on with Swedish investors, who in past years have developed cultlike followings for 3D-printing stocks, biometric sensor companies and most recently Bitcoin.

They are not alone in betting on cannabis companies as more and more countries legalize it for medicinal and recreational purposes.

“That’s where the money is, if there’s a will to continue legalizing markets,” Bornold said. “But if the wind turns, that gigantic market will close as fast as it opened.”

Local stocks have also got caught in reefer madness, even though Sweden will probably be among the last countries on Earth to legalize marijuana. Heliospectra AB, a maker of advanced lighting systems for plants that trades on Stockholm’s alternative market for smaller companies, soared 143 per cent in the first two weeks of the year and is up 39 per cent year-to-date.

“Heliospectra became involved in the rush due to the so-called Klondike thesis, that is, it’s not the gold diggers that make the money, but the people selling the spades,” Bornold said.

While the start of the year was exceptional, Bornold predicts the craze will cool. In total, about 50,000 Swedes traded in cannabis shares on Nordnet and Avanza AB during January, according to Bornold.

“Trading in these shares will most likely continue, but not at this level, we just can’t have more people trading in cannabis shares than in Volvo shares,” he said. “It’s interesting that so many Swedes are prepared to invest in cannabis companies while very few according to polls want to legalize cannabis in Sweden. There doesn’t seem to be a problem in making money from it.”