If taken in the presence of diarrhea, stool softeners do not even aggravate the diarrhea.  They merely retain moisture in stool as it is being formed.  Some stool softeners, even cause liquid stools to gel and none of them take care of “old inventory”  (existing hard feces), and so by any reasonable definition stool softeners are not laxatives.  Examples of stool softeners psyllium seed (Metamucil), Miralax (a new prescription product), methocellulose (many trade names).


A very important rule of thumb is that all irritant laxatives are habit forming.  By in large, if it comes in a small
 package, such as a pill or two, it is an irritant and, therefore, habit forming.  Our bodies respond to a harsh, irritating diet by getting used to it, reducing or eliminating the inconvenience.  This is an advantage if a harsh irritating diet is all that is available.  For example, a missionary in a Mexican village, living off the local economy, will ultimately adjust to such a harsh diet and very nearly cease to be inconvenienced by it similar to the natives of that locality.  Our bodies do not respond differently to irritants depending on our motivation in ingesting them.  Call habit-forming laxatives the back side of a virtue.  A pitfall:  if a bulk laxative has a prefix or suffix added to it’s name such as peri- or –plus, that means that it is spiked with an irritant.  The uninitiated could get the short-term benefit of the irritant on old inventory without awareness of habit and dependence in the more remote future.  Cascara and senna are irritant herbal laxatives.  Phenolphthalein is a synthetic chemical with many uses besides medicine.  It is the active ingredient of many proprietary laxatives such as Ex-Lax, Feen-a-mint and Carter’s little pills.


Which are the non-habit forming laxatives?  They are all called  osmotic laxatives, which mean they extract water from the lining of the intestines by the same inevitable mechanism as cucumbers shrinking to pickles in brine.  There is no way for our bodies to accommodate this extra fluid in the intestines except by pushing it on through.  Any non-poisonous salt with a non-absorbable ion is an osmotic laxative.  Epsom salts (magnesium sulfate) has magnesium and sulfate ions, which are scarcely absorbed.  It tastes bad and is hard to get an effective dose without getting too much.  Sodium sulfate (Glauber’s salt) is not much better.  Sodium phosphate (Fleet’s phospho-soda) is a little more manageable, but we tend to avoid it because the absorbed sodium aggravates dropsy (congestive heart failure) and high blood pressure, and most people who need laxatives are elderly.  Milk of magnesia (magnesium hydroxide) acts as an antacid in the stomach and soothes it.  In the intestine, the magnesium ion does the osmotic work retaining fluid in the lumen until it is eliminated, an enema from the top down.  The bottom line, milk of magnesia is far and away  the most acceptable non-habit forming laxative, but it will probably not become so popular that vodka and milk of magnesia come to be known as a Phillip’s screwdriver.


Mineral oil and proprietary equivalents such as Kondremul are lubricants and not strictly speaking laxatives, but they do lubricate and make a hard stool more easily passed.  A nuisance hazard is that the anal sphincter does not retain them.   Diet salad dressing, made with mineral oil also has this problem.  It is very important to not take oil laxatives at bedtime.  Tiny amounts coating the throat may enter the lungs during sleep.  These oils are so bland that they do not induce cough, so they accumulate in the smallest passages of the lungs.  This occurs gradually over a long period of time and should be easily avoided by those who know about the hazard.  The diet salad dressing taken with meals does not enter the lungs in significant amounts but the mineral oil in it dissolves fat-soluble vitamins and because mineral oils are not digestible these vitamins are also eliminated without absorption.


Castor oil is unique in an interesting way, even though it is seldom used because it is especially disagreeable to take, both for its bad taste and strenuous action, which can scarcely be regulated.  Castor oil is another laxative that is not a laxative but it does become one only after it is digested.  The actual events after swallowing large doses of castor oil is that the little bit of ricinoleic acid formed when digestion of castor oil is just  starting  pushes the rest of the castor oil through the digestive tract so fast that not much more of it is digested, so a rather small dose, but enough to cause near maximum irritation, has essentially the same consequences as an extremely large dose.  In a real sense, castor oil is very poisonous except that it is its own antidote.


Laxatives are unavoidable in many inactive elderly people on a limited diet.  The best way to avoid the need for them, at any age, is to be active physically and include fruits and vegetables with (almost) every meal.


John A. Frantz, M.D.

Chairman, Monroe City Council Board of Health

October 27, 2002