Parietal cells in the gastric lumen secrete acid through proton pumps. Proton pump inhibitors (PPIs) and potassium-competitive acid blockers (pCABs) inhibit proton pumps through different mechanisms. PPIs require activation from acid to bind irreversibly to the pump. In contrast, pCABs bind reversibly without prior activation, leading to a faster onset of action compared to PPIs. pCABs may be preferable to PPIs initially to diagnose acid reflux before more invasive testing. Vonoprazan, a pCAB, was approved in Japan in 2015 for treating erosive esophagitis.