09/13/2026
🐶 Is your dog taking omeprazole (Prilosec)?
Omeprazole is a commonly used acid-reducing drug💊, but a new peer-reviewed study published in the Journal of the American Veterinary Medical Association (JAVMA) is raising an important question about what can happen to the stomach during long-term use.
Researchers studied dogs taking omeprazole for 5 months or longer and found a consistent pattern of changes: a thickened stomach lining with enlarged folds. Biopsies showed overgrowth and enlargement of cells and glands in the stomach lining.
🩺 The changes can look alarming.
The researchers noted that stomach wall thickening can raise concern for “infiltrative disease, severe gastritis, or neoplasia” (cancer). Importantly, this does not mean omeprazole causes stomach cancer. Rather, these medication-associated changes can look similar to cancer or other serious stomach diseases on imaging.
And this isn’t the first research to raise questions about prolonged acid suppression in dogs. Other studies have reported increased gastrin, changes to the gut microbiome, intestinal inflammation, and similar physical remodeling of the stomach lining. A 2026 study documented thickened, irregular “cobblestone-like” stomach folds, gland changes, inflammation, and fibrosis in dogs with prolonged omeprazole exposure.
A prospective trial presented at ACVIM also found 10 of 20 healthy dogs starting twice-daily omeprazole experienced adverse effects, including appetite changes, vomiting, or stool changes; among dogs completing microbiome testing, 12 of 15 trended toward dysbiosis.
Omeprazole💊 can be an important medication for treating G.I. ulcers and specific medical conditions, so don’t stop it abruptly without talking to your veterinarian. If your dog has been taking it for months or years, ask your veterinarian whether it’s still needed and whether continued use should be reassessed.
The big question researchers are now trying to answer: What happens to the stomach when we suppress its acid for months—or even years?
