Nizatidine is a histamine H2-receptor antagonist that inhibits stomach acid production, and commonly used in the treatment of peptic ulcer disease (PUD) and gastroesophageal reflux disease (GERD). Certain preparations of nizatidine are now available over the counter in various countries. Nizatidine has been used experimentally to control weight gain associated with some antipsychotic medication. Antacid preparations such as nizatidine work by suppressing acid mediated break down of proteins, leads to an elevated risk of developing food or drug allergies. This happens due to undigested proteins then passing into the gastrointestinal tract where sensitisation occurs. It is unclear whether this risk occurs with only long-term use or with short-term use as well. Nizatidine proved to be the last new histamine H2-receptor antagonist introduced prior to the advent of proton pump inhibitors.