An unauthorized product with a numbered name is available for sale to Canadians online but a drug maker says it stopped testing it when it was linked to cancers in animal studies.

Health Canada and GlaxoSmithKline  warned Friday of serious risks associated with the unauthorized product GW501516.

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GlaxoSmithKline said it stopped all clinical development of GW501516 when toxicities, including various cancers, were discovered during long-term animal studies. (Sang Tan/Associated Press)

"A compound referred to as GW501516 is being made available for sale to Canadians via the internet," a letter from GlaxoSmithKline (GSK) says.

"This compound may be abused by some athletes for performance enhancement. It is not known if the product available via the internet and sold as GW501516 is actually GW501516 or another compound."

In the statement, GSK said it stopped all clinical development of GW501516 when toxicities, including various cancers, were discovered following routine, long-term animal studies.

The long-term effects of GW501516 in humans are unknown, the letter states.

"Canadians are advised not to use this product under any circumstances and should consult with a health care professional if they have concerns about their health related to its use."

GSK was developing the drug to raise HDL, or good cholesterol, levels but said it stopped in 2006 when the toxic effects in mice and rats were discovered.

The drug is on the World Anti-Doping Agency's prohibited list. In March, the Montreal-based agency revealed some athletes had tested positive for its use.

"The side-effect of this chemical compound is so serious that WADA is taking the rare step of warning 'cheats' to ensure that there is complete awareness of the possible health risks to athletes who succumb to the temptation of using GW501516 for performance enhancement," WADA said at the time.

With files from The Canadian Press