This article was updated on Sept. 20 to reflect actions taken by other countries.

The heartburn drug Zantac has been on the market for decades, and was considered safe enough to be sold over the counter and regularly given to infants.

But on Sept. 13, the Food and Drug Administration said that it had detected low levels of a cancer-causing chemical in samples of the drug, which is also known as ranitidine. The agency advised patients who were taking over-the-counter versions of Zantac to consider switching to other medications.

On Sept. 18, the drug maker Novartis said that its generic-drug division, Sandoz, had stopped distributing a prescription form of ranitidine worldwide as it investigates the issue. Another major generic manufacturer, Dr. Reddy’s Laboratories, also said it was halting distribution.

The companies, including Sanofi, which manufactures the brand-name version, have stopped short of recalling their products in the United States.