Senna !
A plant-based stimulant laxative: its sennosides are activated in the colon and make it contract, usually overnight.
Updated 2026-11-01
Also called: Sennosides, Senna glycosides
Mechanism of action
Senna contains anthraquinone glycosides (sennosides) that are poorly absorbed. In the colon they are hydrolysed to active anthraquinones, which stimulate the enteric nerves and increase the secretion of water and electrolytes, so the colon contracts and the stool softens.
- Sennosides pass the small bowel without being absorbed
- Hydrolysed in the colon into active anthraquinones
- Stimulate colonic nerves and fluid secretion
Pharmacokinetics
- Absorption
- Poorly absorbed
- Metabolism
- Activated by hydrolysis in the colon
- Onset and duration
- Usually 6 to 12 hours by mouth, so it is often taken at bedtime
Indications
- Short-term relief of constipation Constipation and faecal impaction →
- Emptying the bowel before surgery and some procedures
Adverse effects
Common
- Abdominal cramps and discomfort
- Nausea
- Faintness
- Harmless brown discoloration of the urine
Contraindications
- Abdominal pain, nausea or vomiting of unknown cause, or suspected bowel obstruction
- Long-term use in older adults without medical advice
Key interactions
- Mineral oil
- The combination is avoided unless a clinician directs it
- Other oral medicines
- Some senna products are taken apart from other medicines because they can change how those work
What is monitored
- Bowel movements and cramps
- Rectal bleeding
- Duration of use (more than a week needs medical review)
Administration and safety
- Often given at bedtime so the bowel movement comes the next morning.
- Not used for more than a week without medical review.
Nursing care
- Ask about abdominal pain, vomiting or a sudden change in bowel habit before giving it.
- Explain that brown urine can occur and is harmless.
- Report rectal bleeding or lack of effect.
- Encourage fibre, fluids and activity; in older adults, review long-term use with the prescriber.
Pregnancy and breastfeeding
Usually acceptable in pregnancy after checking with a clinician; it can be used while breastfeeding once the baby is at least 1 month old.
Test yourself
Think of the answer, then tap the question to see it.
Where are senna's sennosides activated?
In the colon, where they are hydrolysed to active anthraquinones.
Which colonic finding is linked to chronic use of anthraquinone laxatives?
Melanosis coli, a brown pigmentation of the colon lining.
Why is senna often given at bedtime?
It usually acts in 6 to 12 hours, so the bowel movement comes the next morning.
Related drugs
Related conditions
← Back to the class: Laxatives
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - SENNOSIDES tablet (DailyMed (U.S. National Library of Medicine), 2026); Senna: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2024); Senna: a laxative medicine to treat constipation - NHS (NHS (National Health Service, UK), 2026); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 62 (McGraw Hill, 2025).
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Representative model, for educational purposes only.