Alexandrian senna (Senna alexandrina) is a well-known herbal laxative, traditionally and scientifically used to treat constipation. Its active compounds, called sennosides, stimulate peristalsis in the colon by irritating the colonic mucosa, thereby promoting bowel movements. In the context of "spastic colon," an older term often used for irritable bowel syndrome (IBS) with constipation, senna is sometimes used to relieve constipation symptoms. Several randomized controlled trials and systematic reviews have demonstrated the efficacy of senna as a short-term treatment for constipation, including in patients with IBS-C (constipation-predominant IBS). The European Medicines Agency and other regulatory bodies recognize senna for short-term use in occasional constipation.

However, in spastic colon/IBS, where bowel motility may already be abnormal and where patients may alternate between diarrhea and constipation, stimulant laxatives like senna should be used with caution. Overuse may lead to dependency, electrolyte imbalance, or worsening of symptoms. While there is clinical support for its use to manage constipation, there is limited evidence specifically validating the use of senna for "spastic colon" as a whole syndrome, especially when diarrhea or abdominal cramping predominate. Therefore, while scientific evidence supports senna as a laxative for constipation (including IBS-C), its use in broader "spastic colon" is more limited, and it is not recommended for chronic, daily use.