Sherry Herman was watching TV when the ad popped up on the screen. Lawyers were seeking clients for a class-action lawsuit, suggesting a link between certain heartburn pills and chronic kidney disease — including the beige capsules she’d taken for years.

“And I was like, ‘Oh my gosh, yeah — me!’” said Herman, a 50-year-old homemaker in Dayton, Ohio.

She’d been on a drug known as a proton pump inhibitor (PPI) for acid reflux disease since 2004. Thinking it was a “very safe drug,” she had taken the prescription pills for a decade, even though the label recommended four to eight weeks.

Then, in 2014, she was diagnosed with chronic kidney disease. “It came as a huge shock because no one in my family has it,” she said. She had no risk factors for the condition, such as poorly controlled high blood pressure.

A growing body of research suggests the blockbuster drug that helped her stomach may have left her — and a number of patients like her — with a potentially much more serious medical problem.

Recent research has linked the proton pump inhibitors, or PPIs, to serious side effects, including chronic kidney disease, and recently filed lawsuits allege, among other things, that the manufacturers should have known of their potential harms. The risk of chronic kidney disease is as much as 50 percent higher in people who’ve taken the drug compared with those who’ve not — although no causative link has been proven and manufacturers insist they are safe.

The drugmakers strongly defend their products. AstraZeneca is “confident in the safety and efficacy of Nexium and Prilosec when used in accordance with the FDA approved label,” said spokesman Abby Bozarth, in an emailed statement.

Proton pump inhibitors, such as Nexium and Prilosec, among other brands, are blockbusters in the U.S. With 15.3 million prescriptions written in 2013 alone, they are considered highly effective at relieving gastroesophageal acid reflux as well as preventing and treating ulcers. Widely advertised, they are frequently prescribed for even minor indigestion, with serial renewals leading to chronic use — even though they were approved as safe by the Food and Drug Administration only for short-term treatment.

Studies have shown that PPIs could be prescribed unnecessarily as much as two-thirds of the time. And it’s not uncommon for patients to take the heartburn pills for years, even though their labels recommend limiting treatment to a few weeks or a few months. The result has been sales worth many billions of dollars a year for pharmaceutical companies, according to commercial intelligence firm EvaluatePharma.

Tens of millions of Americans take the drugs, whether in prescription or over-the-counter formulation. Given those numbers, critics say that even the suggestion of risk is a problem for a drug that is overprescribed by doctors and used inappropriately by patients.

“When patients complain of gastrointestinal distress, it’s easy to just prescribe a PPI,” said Steven Chen, a doctor of pharmacy and associate dean for clinical affairs at the University of Southern California School of Pharmacy. Once patients start taking the drug, it’s easy to “forget that they may not need to be on it that long.”