Milk of Magnesia is used in constipation.

Milk of Magnesia works by drawing water into the intestine through osmosis, which makes the stool soft and easier to pass.

Dehydration

• Avoid taking a Milk of Magnesia for more than 1 week, unless prescribed by the doctor, as it leads to dependency on the laxative action to produce a bowel movement. 
• Together with Milk of Magnesia, fiber rich diet containing whole grain bread and cereals, bran, fruits and green leafy vegetables, is essential to maintain healthy bowel function.
• A Milk of Magnesia should preferably be taken at bedtime because it requires 6 to 8 hours to show impact.
• Notify your doctor if you are on a low-sugar diet because the Milk of Magnesia contains sugars.
• Take Milk of Magnesia after 2 hours from other medicines, as it may interfere with the absorption of other medicines.