That burning feeling in your chest after you eat a heavy meal could be heartburn. Or it could be worry over the drugs you’ve taken to treat that heartburn. Among the top medical stories of 2019 was the discovery of contaminants in common medicines, and ranitidine—best known as Zantac—took up a large share of those headlines. A cancer-causing substance known as NDMA has been repeatedly found in one of the most popular antacid drugs in the United States.

The scary news continues in 2020. On Wednesday, the Food and Drug Administration announced voluntary recalls of prescription forms of ranitidine by two generic drug companies, Appco Pharma and Northwind Pharmaceuticals, bringing the total number of ranitidine recalls to 14 in the past five months. The agency also reported that Mylan Pharmaceuticals recalled three lots of Nizatidine (Axid), a similar drug, again because of NDMA.

This week’s recalls are a new cause for alarm for the 15 million Americans who take ranitidine at prescription levels, and the millions more who regularly take lower-dose, over-the-counter versions. More than 60 million Americans experience heartburn at least once a month. Zantac was once the best-selling drug in the world.

Bianca Ryan, the season 1 winner of America’s Got Talent, took to Twitter after the voluntary recalls this fall: “I'm literally hyperventilating, like, I've been taking Zantac every single day for the last 10 years for my GERD,” she wrote, referring to gastroesophageal reflux disease, a frequent or more serious form of heartburn, which occurs when acid from the stomach flows up into the esophaagus “So—what do I use now?! And they found what in it?!”

For people worried about past use of Zantac and cancer risk, here’s some back story and a bit of perspective.

Last year, Adam Clark-Joseph, cofounder of the mail order pharmacy Valisure, ordered ranitidine syrup, prescribed to treat reflux in his infant daughter. The pharmacy distinguishes itself by testing every batch of drugs it sells for impurities; earlier, it had found a potential carcinogen in valsartan, a blood pressure medicine. When the ranitidine tested positive for NDMA, Valisure tested other formulations from other manufacturers. “Every batch of every bottle of every manufacturer showed the same results, tremendously high formation of NDMA,” says CEO David Light.

Light says the findings point to an instability with the drug that, in the right conditions, could produce NDMA—for example, if heated. (Valisure heated its ranitidine to 130 degrees Celsius, or 266 degrees F. A car on a hot summer day could reach 140 F.) Valisure reported the results to the FDA, which took exception to the testing methods, saying that its testing at lower temperatures had resulted in much smaller amounts of NDMA. Still, the agency responded to the larger issue, announcing nine voluntary recalls on September 13 with the explanation that “early, limited testing has found unacceptable levels of NDMA” impurities in samples of ranitidine. Even as it argued that a “third-party laboratory” used a method “not suitable for testing ranitidine,” it said it would update its own investigations (without adding heat).

Light stands by Valisure’s testing methods. “We used those conditions to underscore the point that it’s fundamentally unstable,” he says. Valisure also conducted tests with simulated gastric fluid (at body temperature, 37 degrees Celsius) and added sodium nitrite, simulating a diet with high levels of the common preservative found in processed meats, and found high levels of NDMA. The nitrite is an important component (the N) in the creation of NDMA. (Some vegetables, smoked fish, and dairy products also contain nitrates and nitrites.)