TORONTO -- Health Canada has recalled even more ranitidine medications while it continues to investigate levels of an impurity known as N-nitrosodimethylamine (NDMA) in the drugs.

According to the on Friday, Dominion Pharmacal, Laboratoire Riva Inc., Pharmascience Inc. and Vita Health Inc. are all recalling batches of their prescription and over-the-counter products 鈥渁s a precautionary measure.鈥

Prescription ranitidine drugs are commonly used for treating and preventing ulcers in the stomach and intestines. They are also used to treat acid reflux and heartburn associated with acid indigestion and sour stomach.

The recalls are part of an ongoing recall of 27 ranitidine products so far. Last month, Health Canada announced it was collaborating with the U.S. Food and Drug Agency and the European Medicines Agency in investigating these drugs.

More details on affected products from each company can be found on Health Canada鈥檚 website.

The impurity NDMA is concerning because it鈥檚 been classified as a probable human carcinogen, which means long-term exposure to unsafe levels could increase a person鈥檚 risk of cancer, according to a Health Canada release.

The government agency urged people taking prescription ranitidine, including recalled products, shouldn鈥檛 stop taking it until they鈥檝e spoken to their doctor or health care provider, 鈥渁s the risk of not treating the condition may be greater than the risk related to NDMA exposure.鈥