Which laxative type is known for acting immediately?

The chosen answer, bisacodyl, is classified as a stimulant laxative, which is known for its rapid onset of action. Stimulant laxatives work by directly stimulating the intestinal walls, promoting peristalsis (the contractions that move contents through the intestines), and typically induce a bowel movement within 6 to 12 hours after administration. This makes bisacodyl particularly effective for situations requiring quick relief from constipation.

In contrast, the other options have different mechanisms and timelines for action. Magnesium hydroxide, for instance, is an osmotic laxative that draws water into the intestines, providing relief usually within 30 minutes to 6 hours, which is slower than bisacodyl's effects. Sennosides, another stimulant laxative, can also act relatively quickly but may not consistently induce immediate effects as bisacodyl does. Psyllium, on the other hand, is a bulk-forming laxative that requires time for the fiber to swell and promote bowel movements, often taking a day or more to be effective. Thus, bisacodyl is uniquely recognized for its immediate effect among the listed options.