A dietary supplement is being voluntarily recalled in Canada after it was found to contain an undeclared prescription medication, health officials say. Officials at Health Canada said Stiff One Hard 169 -- currently being offered in retail locations in several provinces and on the Internet -- contains thiodimethylsildenafil, an undeclared substance similar to the prescription medication sildenafil, better known as Viagra, which treats erectile dysfunction. Stiff One Hard 169 is being promoted as a dietary supplement and may pose serious risks to the health of Canadians, particularly those with heart problems, those at risk of stroke or those taking any nitrate drug such as nitroglycerine. Officials cautioned consumers to report any adverse reaction potentially related to the product to Health Canada and consult a doctor if they have used the product or are concerned about their health. Products containing sildenafil should never be used by people taking any kind of nitrate drug because it can cause potentially life-threatening low blood pressure, health officials said. Individuals with heart problems including high blood pressure, a history of heart attack, stroke, abnormal heart beat or chest pain are at higher risk of cardiovascular side effects if they engage in sexual activity -- including if they use sildenafil to help them achieve an erection, Health Canada said.