The U.S. Food and Drug Administration said Wednesday it was requesting makers of all versions of heartburn drug Zantac to remove the products from the market immediately due to the presence of a probable carcinogen.

French drugmaker Sanofi SA's Zantac and some generic versions of the treatment, also known as ranitidine, have been recalled over the last year due to possible contamination with N-nitrosodimethylamine (NDMA).

The FDA said it had determined that NDMA in some ranitidine products increases over time and when stored at higher than room temperatures, resulting in consumer exposure to unacceptable levels of the impurity.

"We didn't observe unacceptable levels of NDMA in many of the samples that we tested," said Janet Woodcock, director of the FDA's Center for Drug Evaluation and Research.

"However, since we don't know how or for how long the product might have been stored, we decided that it should not be available."

The FDA also said consumers taking over-the-counter ranitidine should stop taking the drug and not buy more, and those taking prescription ranitidine should ask their doctor about other options before discontinuing treatment.

Last year, Health Canada advised consumers:

Talk to your doctor or pharmacist at your earliest convenience about alternative, non-ranitidine treatment options appropriate for your health circumstances.

Individuals taking a prescription ranitidine drug, including a recalled product, should not stop taking it unless they have spoken to their health-care provider and obtained alternative treatment, as the risk of not treating the condition may be greater than the risk related to NDMA exposure.

"Health Canada continues to work with companies and international partners to understand the root causes of nitrosamines in drugs," the regulator said in an email Wednesday.

Health Canada added it will take action if a risk to Canadians is identified, including informing the public.