Currently four major groups of laxatives.
The goal of all laxatives is tomorrow increase stool water content, directly by osmotic or intestinal secretory means by accelerating bowel transit, thereby increasing fluid absorption.
[Standard laxatives include: fiber/bulk agents that cause retention of water in stool-psyllium and methylcellulose are examples, stool softeners that are detergents and trap water in the stool and docusate is an example, osmotic laxatives that pull water into the stool and include lactulose, sorbitol, magnesium citrate and polyethylene glycol, stimulant laxative which increase contraction of the intestinal muscle and increase peristalsis with bisacodyl and senna as examples.
Osmotic laxtives reduce fluid absorption by the intestine, thereby increasing the water content of stools.
Stimulant laxative promote colonic motility through direct effects in the epithelial, nerve or smooth muscle cells, resulting in an increase in unabsorbed water in stools.