Senna is a stimulant laxative derived from the leaves and pods of plants in the Senna species (especially Senna alexandrina).
- Mechanism of action:
- Contains sennosides (natural anthraquinone glycosides)
- Sennosides are metabolized by colonic bacteria into active compounds (rhein anthrone)
- These compounds stimulate the myenteric plexus (Auerbach’s plexus) → increases peristaltic contractions in the colon
- Also promotes secretion of water and electrolytes into the bowel lumen → softens stool
- Onset of action:
- Oral: 6–12 hours (typically taken at night to produce effect next morning)