What types of drugs lower stomach acid?

The three main categories of acid lowering drugs are antacids, Histamine Type 2 Receptor Antagonists (H2 Blockers), and Proton Pump Inhibitors (PPI's).  They work by 3 different mechanisms.  Antacids neutralize stomach acid that has already been formed.  Since Histamine can stimulate gastric acid secretion, H2 Blockers are used to block a special Histamine Receptor on the surface membrane of the gastric Parietal Cells (a specialized type of cell in the lining of the stomach which makes Hydrochloric Acid).  Proton Pump Inhibitors work inside the Parietal Cells to block the final step of Hydrochloric Acid production.  Since overnight acid secretion is mediated by Histamine, H2 blockers work best when taken at night.  Proton Pump Inhibitors block food-stimulated stomach acid and work best if taken before a meal.  In fact, Proton Pump Inhibitors are activated by food; if a person takes a PPI and does not eat within the hour, there is much less acid lower effect from the drug.