Say that you are shopping for something over-the-counter that will relieve constipation. In the health food aisle you notice a number of teas and capsules containing senna leaf, and they look quite promising.
But, as with any herbal remedy for minor conditions, before you make your purchase you ought to be aware of how the product works and its possible side effects.
A page about senna on the National Library of Medicine website explains that the herb (Cassia acutifolia) has been approved by the Food and Drug Administration as a nonprescription laxative. The fruit of senna is considered to be milder than the leaves, but many products use the leaves.
Senna typically does the trick for constipation because the chemicals in it, called sennosides, irritate the lining of the colon and force contractions in the bowel.
The Library of Medicine page, using the Natural Medicines Comprehensive Database, gives effectiveness ratings for various uses of senna.
For instance, for constipation it is rated "likely effective." For bowel preparation before a colonoscopy, it is rated "possibly effective," although doctors usually prescribe sodium phosphate or another product for colonoscopy prep.
For hemorrhoids, irritable bowel syndrome and weight loss, senna is considered to have insufficient evidence behind it to rate effectiveness.
As a laxative, though, senna raises concerns about possible overuse or abuse by those desperate to lose weight, as well as the risk of creating a laxative dependency.
On his alternative-health website, DrWeil.com, Dr. Andrew Weil says that certain laxatives, including senna, are "irritant types." They induce bowel movements "quickly, sometimes violently, by irritating the bowel."
Sometimes the constipation gets worse, he says, in a question-and-answer column about natural remedies for constipation.
Among the signals for discontinuing use of senna are diarrhea, cramps, watery stools and abdominal pain. The American Herbal Products Association warns against long-term use of senna leaf and urges women who are pregnant or nursing to get advice from a health care practitioner before taking senna.