Fast and effective relief: Geri-Care Milk of Magnesia offers fast overnight relief from occasional constipation with its powerful laxative-antacid formula.. Original flavor.. There are 1,200 milligrams of magnesium hydroxide in each 15 mL dose.. Compare to the active ingredient in Phillips' Milk of Magnesia – a registered trademark of Bayer.. 1-pint bottle will likely be enough to last your family for a while..