Milk of magnesia, also known as magnesium hydroxide, is a type of saline laxative that is often used to treat constipation. It contains magnesium, a naturally occurring mineral needed for many body functions, especially the nerves and muscles. Milk magnesia can be fast-acting, meaning that it would make you feel a bowel movement from 30 minutes to 5 hours after taking the drug. It is easy to purchase the milk of magnesia over the counter without any prescription. You should avoid giving the medication to children under two years old unless suggested by a healthcare provider. Also, this is not a long-term treatment for constipation, especially in pregnant women. 
Milk of magnesia basically works by pulling water from nearby tissues in the body to the bowel. This helps moisten and soften the stool, making it easier to move the stool in the bowels. It is a common OTC medication made to help the digestive system work smoothly. The stool-softening effect would make it easier for you to visit the toilet. Also, as a saline laxative, magnesium hydroxide would help you increase the frequency of bowel movements.