Antacids are usually nonprescription medications like the aluminum-magnesium combination (Maalox) or the calcium based (Tums). They can be indicated for uncomplicated peptic ulcer and gastric hyperacidity.
But with GERD, they can be only used as aids or supplements for the rapid relief of its symptom as heartburn. More to this, although they can neutralize the acid in the stomach, that there is no acid to reflux, antacids action is brief. They are emptied from stomach so quickly, that the acid can re-accumulate in less than an hour.