Senna
A plant-derived stimulant laxative (sennosides) for short-term relief of constipation, usually taken at night.
Also called sennosides (US label name for its active glycosides).
Drug card
- Class
- Stimulant laxative
- How it works
- Stimulating the colon lining to push stool along and secrete water
- Used for
- Short-term relief of constipation
- Known for
- Abdominal pain and cramps
- Dark pigmentation of the colon lining (melanosis coli)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does senna work?
Its sennosides are glycosides that pass the upper gut unabsorbed and are not split by human enzymes; colonic bacteria convert them to the active rhein anthrone. This speeds colonic transit and makes the colon secrete water and salts while absorbing less, so a bowel movement follows about 6 to 12 hours later.
Like other stimulant laxatives: Stimulant laxatives are turned into their active forms in the gut and act directly on the lining of the large bowel. They set off propulsive contractions of the colon and make it secrete water and salts while absorbing less, so stool arrives sooner and softer: about 6 to 12 hours after a tablet, and within an hour after a bisacodyl suppository.
Uses
What is senna used for?
- Short-term relief of constipation
Side effects
Side effects of senna
- Abdominal pain and crampsKnown for
- Dark pigmentation of the colon lining (melanosis coli)Known for
- Diarrhea
- Harmless yellow-brown or red-brown urine
- Low potassium with long-term useSerious
- DehydrationSerious
- Sluggish, laxative-dependent bowel after long overuse
- Itching, hives and rash
- Liver injury after chronic overdoseSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Avoid with bowel obstruction, appendicitis, inflammatory bowel disease or unexplained abdominal pain.
- Low potassium from overuse raises the risk with digoxin and antiarrhythmics; diuretics, steroids and licorice add to the loss.
- Use for about a week at most without finding the cause of the constipation.
Remember it
A way to remember it
Stimulant laxatives make the colon squeeze, and squeezing cramps.
Senna and bisacodyl act on the colon lining to trigger strong propulsive contractions and secretion, which is why abdominal cramps are their classic side effect.
Written for biofideX
Its class
Stimulant laxatives
Other stimulant laxatives with a card:
Easily mixed up with osmotic laxatives.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Sennosides syrup: label (DailyMed)
- Sennosides 7.5 mg tablets: SmPC (eMC)
- Senna Fruit (NCI Thesaurus)
- Senna (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Stomach and gut
Senna is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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