US retailer CVS has become the latest to suspend the sale of a heartburn drug being investigated for links to cancer.
It follows concern in several countries over the presence of impurities in Zantac and other ranitidine products.
Canada and France have already announced Zantac recalls. The US and the European Union are investigating.
Health authorities say there is no immediate risk, but patients have been advised to consult a doctor who can prescribe alternatives to ranitidine.
On September 13, both the US Food and Drug Administration and the European Medicines Agency (EMA) published their decisions to review the presence of N-nitrosodimethylamine (NDMA) in medicines containing the drug ranitidine.
NDMA is classified as a probable human carcinogen on the basis of animal studies. It is not expected to cause harm when ingested in very low levels.
Ranitidine products are used to reduce production of stomach acid in patients with conditions such as heartburn and stomach ulcers.
They are available over-the-counter and on prescription.