Antacid combinations of magnesium and aluminium salts are superior to single component preparations because.
(Ref: KDT 6/e p635) Mg (OH)2 has a quick onset whereas Al (OH)3 acts for a long time. Magnesium salts cause osmotic diarrhea whereas aluminium salts cause constipation. Combination of these two agents minimizes the impact on bowel movements.