Ontario Provincial Police (OPP) launched an investigation into how the drug found its way into the chocolate treats given to elderly people in the tiny Ontario township of Whitestone.
Police said 10 people needed medical attention after eating the brownies, with some saying they felt dizzy and disoriented, and others experiencing nausea and vomiting.
OPP constable Miles Loach told CBC News that police officers would try to track down where the brownies came from.
“These luncheons are catered,” he said. “It’s still part of the investigation whether that was what happened … [that] somebody brought the wrong batch or somebody spiked them.”
The incident happened at the community centre in Whitestone, a community of just over 900 people around 185 miles north of Toronto.
James McNurdo, a semi-retired man involved organising the monthly lunch club, said the brownies were served buffet-style.
“I’ve done these events for a number of years for this particular group so, obviously, I’m as mortified as anybody,” he told The Globe and Mail. “We’ve got to get to the bottom of this, no doubt about it.”
Mr McNurdo added: “The rumour mill is in overdrive.”
Police had initial concerns some of the lunch club attendees might have been allergic to the substance – or could even have even driven home inadvertently stoned.
But Mr Loach said no-one had suffered any seriously adverse effects from the cannabis-laced cake. OPP officers got the names of everyone present at the lunch and made follow-up calls to make sure everyone was okay.
Canada legalised and regulated cannabis last year. But there are criminal offences related to administering a noxious substance to “cause harm” or “aggrieve”.