, the GI sphincter no longer feels a need to do its job, which is, keep
acid where it belongs...in the stomach. It relaxes and allows
acid to creep into the esophagus. Only, since the drug reduces the acid, you no longer feel it.
Pharmaceutical companies that make these drugs love this. The short-term 'cure' necessitates the continued use of their products. I've heard a lot of people complain that "as soon as I stop taking my [acid reducer of choice], I get heartburn.