The objective of a laxative is to promote defecation. There are a number of agents. They each have different mechanisms.
- A bulk-forming agent like methylcellulose or psyllium hulls do just that, form bulk, which increase intestinal motility. Psyllium hulls are a favorite of mine, because it also helps lower cholesterol and can be used long-term.
- If the laxative is osmotic or saline, such as magnesium ion, then the mechanism is to draw water from mucosa using high ion concentration to create luminal osmotic pressure.
- An irritant or stimulant agent, such as anthraquinones from senna or aloe vera latex, bother the intestinal mucosa and promote secretion and enhance distention. They can be dangerous. High doses of anthraquinones inhibit electrolyte reabsorption and induce depletion of potassium while long-term use can irritate mucous membranes.
- In addition, when stools are hard, sometimes a different kind of laxative is used such as docusate potassium, which helps soften stools by emulsifying, mixing water and fat. This can also be promoted by soluble fiber such as guar gum.
Nowak TJ, Handford AG. Pathophysiology: Concepts and Applications for Health Professionals. New York: McGraw-Hill, 2004.
Jellin JM, Gregory PJ, and et al. Pharmacist’s Letter/Prescriber’s Letter Natural Medicines Comprehensive Database, 10th ed. 2008. Stockton, CA, Therapeutic Research Faculty. 2. Davis RH.