What is the mechanism of action of saline/hyperosmotic laxatives?

The mechanism of action of saline or hyperosmotic laxatives is primarily based on their ability to attract and retain water within the intestines through osmotic pressure. When these substances are ingested, they draw water into the intestinal lumen, increasing the volume of the intestinal contents. This increased volume adds bulk to the stool, which encourages intestinal stretching and, in turn, promotes bowel movements.

The osmotic effect is particularly important because it not only helps to hydrate the stool, making it softer and easier to pass, but it can also lead to an acceleration of the transit time through the intestines. By increasing the fluid content, saline and hyperosmotic laxatives effectively enhance the natural process of defecation, making them effective treatments for constipation.

This mechanism differs from other laxatives that may rely on different modes of action, such as stimulating nerve pathways to induce contractions in the intestines or adding bulk through fiber, which are not the primary functions of saline and hyperosmotic laxatives.