(CBS NEWS) Prolonged use of heartburn drugs is associated with increased risk of kidney damage, researchers say. A new study, published in the journal Kidney International, looked at adults who use proton pump inhibitors (PPI) – sold under brand names like Prevacid, Nexium and Prilosec – as well as users of H2 blockers like Zantac or Pepcid.  

Over the course of five years, the 125,596 PPI users studied were at higher risk for chronic kidney disease and acute kidney injury than the H2 blocker users.

These findings could impact an estimated 15 million Americans who use these prescription PPI medications for heartburn and acid reflux. And experts are concerned that patients with kidney problems may not experience warning signs.

“Chronic kidney disease is not one that has symptoms or signs until it’s too late. So obviously worrisome,” CBS News contributor Dr. David Agus said Thursday on “CBS This Morning.” “These were the prescription brands but they’re also available over-the-counter. And over-the-counter, classically, people aren’t even checked for kidney problems.”

Heartburn can occur when acid from the stomach goes back up into the esophagus. The lower esophageal sphincter (LES), a “valve” between the stomach and esophagus, would normally prevent the acid backwash. But Agus said some people’s diets could weaken the LES.

“So avoid the fatty foods, avoid eating too much, alcohol, tobacco. They can all make that valve weaker to allow acid to come into the esophagus,” Agus said. “So try avoidance as much as possible and then talk to your doctor, maybe taking something else for this may be helpful or look at other ways of avoiding the reflux.”

Agus said there are surgeries and more “aggressive routes” to prevent acid reflux, but avoidance is best. 

CBS News reached out to Pfizer (which makes Nexium and Protonix), Takeda (maker of Prevacid), and P&G (Prilosec) for comment on the risks. Pfizer referred us to the Consumer Healthcare Productions Association, who provided a statement on over-the-counter PPIs: 

“Millions of people rely on safe and effective over-the-counter (OTC) proton pump inhibitors (PPIs) to relieve their frequent heartburn symptoms. The article published in Kidney International does not assess OTC PPIs, rather, it focuses on prescription strength PPIs which are used at higher doses and for longer durations than OTC PPIs. Currently available safety data and cumulative experience on the use of OTC PPIs does not warrant any revision of clinical practice, and the study’s authors are not recommending any changes to the well established guidelines for safe and effective use. 

OTC medicines, including PPI products, are regulated by the Food and Drug Administration’s (FDA’s) Center for Drug Evaluation and Research. Each OTC PPI product has been extensively reviewed by FDA before approval. Consumers should read and follow OTC Drug Facts labels closely to understand what each medicine is used for, to assure it is appropriate for their symptoms, to ensure proper dosing, duration of use, and to avoid drug interactions. Any severe or persistent symptoms should be immediately reported to a healthcare provider. 

For more than ten years, OTC PPI products have provided an important health benefit to consumers and a direct cost savings for the healthcare system. Research by CHPA and the Nielsen Company shows 94 percent patient satisfaction with OTC heartburn medications, and indicates that OTC therapy saves patients an average total of $174 each in office visits and medication costs annually.”