Constipation means having infrequent bowel movements with stools that are hard and sometimes painful to pass. Over-the-counter fiber products such as psyllium (brand name Metamucil®), polycarbophil (FiberCon®) and methylcellulose (Citrucel®) are usually the best first choice for constipation. They add bulk to the stool and stimulate the intestines to contract. These laxatives work gently and slowly and are safe for long-term use, though it may take one to three days to notice an effect. It's very important to take each dose with a full glass of fluid and to drink plenty of water throughout the day. Stool softeners such as docusate sodium (Colace®) often help to prevent constipation. They are generally taken on a daily basis and may take a few days to work. Be sure to consult your doctor if you don't see results after one to two weeks of using a stool softener. Another option is milk of magnesia, which targets upset stomach and constipation. As a laxative, it pulls water into the intestine and increases the urge to have a bowel movement. It can take anywhere from 30 minutes to one hour for results. For constipation, the usual dose is two tablespoons taken once or twice daily. Do not use milk of magnesia for more than two weeks unless your doctor prescribes it. Bisacodyl (Dulcolax®) and senna (Senokot®) should be considered a last resort to treat occasional constipation. These products work by stimulating the bowel. They generally take from six to eight hours to take effect. You shouldn't use this type of laxative frequently or for long periods of time, since they don't treat the cause of constipation and may cause the bowel to become "lazy," which can lead to severe constipation over time.
Sources: Pharmacotherapy: A Pathophysiologic Approach. Appleton and Lange, 1999.