People who bought an unauthorized natural health product called Novodalin B17 claiming to treat cancer should stop using it and contact their doctor for follow-up, Health Canada says.
The regulator does not allow cancer treatment claims for natural health products.
Novodalin B17 is sold online and "poses serious risks to health" because it is labelled to contain apricot kernel extract, Health Canada says.
In turn, the kernels may contain amygdalin, which has the potential to release cyanide when ingested.
"The concentration of amygdalin is unknown at this time, however, ingesting low to moderate amounts of cyanide may lead to serious adverse health consequences and high doses may be lethal," Health Canada said.
Health Canada has asked the online seller to stop sale and warns it will take further action if more risks are identified.
The pills were still on sale online on Wednesday advertised as $114.99 for 100 pills.
Health products have been authorized for sale by Health Canada have an eight-digit DIN, a DIN-HM or a NPN.