Health Canada said companies that market ranitidine drugs, including the popular heartburn medication Zantac, have been asked to stop distribution in Canada after a probable human carcinogen was detected in some of the drugs.

The medication that’s already in stores will continue to be sold, said Health Canada in an alert Tuesday, as ranitidine drugs have not been recalled altogether.

However, one company that markets the ranitidine in Canada, Sandoz Canada, has recalled its version of the drug after tests found levels of an impurity above what would be considered safe if taken over the long term.

It’s believed that long-term exposure to the impurity that was detected -- N-nitrosodimethylamine or NDMA -- at levels higher than what’s considered safe could increase a person’s risk for cancer, according to Health Canada.

The move comes days after U.S. officials announced they were investigating Zantac and generic versions after detecting a chemical that is a probable carcinogen.

Health Canada noted that people are exposed to low levels of the chemical in common foods and drinking water, but it isn’t believed to be harmful at low levels.

It also said people who are prescribed ranitidine shouldn’t stop taking it without speaking to a doctor about an alternative treatment, and those who use over-the-counter versions who want to explore other options should speak to a doctor or pharmacist.

A full list of versions of ranitidine marketed in Canada is available by searching a database on Health Canada’s website.