Alexandrian senna (Senna alexandrina) is widely used as a stimulant laxative, with its primary active components being sennosides. These compounds are well-studied for their ability to stimulate peristalsis in the colon, making senna effective in treating atonic colon (a form of constipation characterized by reduced muscle tone and motility in the colon).

Numerous clinical trials and pharmacological studies have validated the efficacy of senna in managing constipation, including cases classified as atonic or non-obstructive. The mechanism involves the irritation of the colonic mucosa and direct stimulation of enteric nerves, which increases peristaltic contractions and promotes bowel movements. Senna also reduces water reabsorption in the colon, softening stools.

Senna is included in many pharmacopeias and recommended by authoritative bodies (such as the World Health Organization) for short-term relief of constipation, including in elderly or bedridden patients with atonic colon. However, long-term or excessive use can lead to dependency or electrolyte imbalances, so guidelines emphasize short-term use only.

In summary, Alexandrian senna is scientifically validated for the treatment of atonic colon and related forms of constipation, with a substantial body of evidence supporting its efficacy and mechanism of action.