antacid /antas″id/ [Gk, anti, against, acidus, sour] , 1. opposing acidity. 2. a drug or dietary substance that buffers, neutralizes, or absorbs hydrochloric acid in the stomach. Nonsystemic antacids containing aluminum and calcium are constipating; those containing magnesium have a laxative effect. Systemic antacids such as sodium bicarbonate are rarely used.
