Saskatoon police say charges include trafficking and possession of the proceeds of crime.
Insp. Dave Haye with the Saskatoon police says Compassion Club founder Mark Hauk had been warned he'd be arrested if he was found breaking marijuana laws.
Haye says the club had been operating as if it was a legitimate business but he says "they were marijuana trafficking, so they're drug traffickers."
Last month, Hauk said he knew that opening a storefront for medical marijuana was illegal, but said it was the only option that made sense, because otherwise patients have to order it online and wait for their prescription.
The operation, called Project Fextern, was an investigation by the Saskatoon Integrated Drug Enforcement Street Team and Integrated Organized Crime North.
The four people arrested are expected to appear in court on Friday.
Prime minister designate Justin Trudeau has promised to legalize and regulate marijuana, not just for medicinal purposes but for recreational use as well, but there's been no word on how long that will take.