Milk of magnesia is magnesium hydroxide. It's a powerful base. Though it's not well absorbed, you can absorb enough to give your acid-base physiology a big and continual workout. It will also pull significant water from the body because your not taking it as an isotonic solution, so that gives your water balance mechanism a workout.Miralax should have much less effect your water balance.you lose only some of what's already in your gut and it has no effect on your acid-base balance. It's the safest pharmacological laxative.quote:Why would this new prescription medication Miralax be considered superior?