A substance that could cause cancer has been found in the heartburn drug Zantac and several other antacids, the Food and Drug Administration announced Friday.

The agency said preliminary tests found low levels of a substance known as NDMA, classified as a “probable human carcinogen,” in ranitidine products that treat heartburn and stomach ulcers, according to the statement, which only named brand drug Zantac.

Despite the warnings, the FDA said it was not calling for people to stop taking ranitidine drugs or recalling them from the market, but will evaluate the risk.

“Although NDMA may cause harm in large amounts, the levels the FDA is finding in ranitidine from preliminary tests barely exceed amounts you might expect to find in common foods,” the statement claimed.

“The agency will provide more information as it becomes available.”

NDMA has been labeled by the FDA as a cancer-causing substance but it also occurs naturally in water and foods such as meat, vegetables and dairy products.

The same contaminant was found in some blood pressure drugs last year, sparking a mass recall.