At a glance: Senna leaf is a stimulant laxative prepared from Senna alexandrina Mill. (older names include Cassia senna L. and Cassia angustifolia Vahl). Its major laxative constituents are hydroxyanthracene glycosides known as sennosides. Gut bacteria convert sennosides to active metabolites, particularly rhein anthrone, which act mainly in the colon to increase motility and secretion. Senna has a clear role in short-term constipation, but regular long-term use without clinical supervision can cause diarrhoea, electrolyte disturbance and impaired bowel function.[1][2][3]
Botanical profile
- Accepted medicinal name: Senna alexandrina Mill.
- Older botanical names: Cassia senna L.; Cassia angustifolia Vahl.
- Common name: senna.
- Family: Fabaceae.
- Medicinal part covered here: leaf.
- EMA herbal drug name: Sennae folium.[1]
Senna pods are also used medicinally and have a separate EMA monograph. Leaf and pod preparations share important hydroxyanthracene constituents but should still be identified correctly when citing a product or study.[4]
Major constituent groups
The pharmacologically important constituents are hydroxyanthracene derivatives, particularly the dianthrone glycosides:
- sennoside A;
- sennoside B;
- related sennosides and anthranoid glycosides; and
- smaller amounts of flavonoids, mucilage and other plant constituents.
The parent sennosides are not simply absorbed and acting systemically like a conventional tablet. Their activation depends importantly on the colon and its microbiota.
How senna works
Sennosides reach the lower gastrointestinal tract, where bacterial enzymes convert them to metabolites including rhein anthrone. Experimental and pharmacokinetic work indicates that rhein anthrone acts locally in the colon, promoting propulsive activity and increasing secretion while reducing net water absorption.[5][6]
Prostaglandin signalling, epithelial transport and changes in colonic motility all appear to contribute. This is a useful pharmacology example because the laxative effect is not adequately described by saying that senna simply “irritates the bowel”.
Traditional use
Senna has a long history in Arabic, Unani and later European medicine as a purgative for constipation and for deliberate bowel evacuation. Leaf and pod preparations became established pharmacy laxatives because they produce a reliable stimulant effect on the colon.
A herbalist’s perspective on senna
Herbalists do not routinely turn to senna as a first choice for ordinary constipation. It is rather like using a sledgehammer to open a bottle: it will often get the job done, but it can be far more forceful than the situation requires. In practice we usually look at why the bowel is sluggish and choose a gentler approach where appropriate. For example, bitter herbs such as gentian may be used where poor digestive tone is part of the picture, rather than simply forcing bowel evacuation. Senna still has a useful place when a stimulant laxative is genuinely the right tool.
EMA regulatory assessment
The European Medicines Agency HMPC has a final EU herbal monograph for senna leaf in the therapeutic area of constipation. Revision 1 was published in April 2020 and an assessment-report addendum followed in April 2022.[1]
The monograph concerns defined senna-leaf preparations for short-term treatment of occasional constipation. It is not an endorsement of prolonged “cleanses”, weight-loss use or habitual laxative use.
Constipation: what is senna actually for?
Senna is a stimulant laxative. The NHS describes it as stimulating the muscles lining the gut and notes that it commonly takes around eight hours to work.[3]
It can therefore be useful when short-term stimulation of bowel movement is appropriate. Persistent or recurrent constipation deserves attention to possible causes, medication effects, hydration, fibre, mobility and underlying disease rather than indefinite escalation of stimulant laxatives.
“Detox” and weight-loss claims
Senna causes bowel evacuation; that is not the same thing as removing unspecified “toxins” from the body. Any short-term drop on the scales after a laxative reflects stool and fluid loss rather than loss of body fat.
Marketing senna as a slimming tea or detox product obscures its actual pharmacology and can encourage misuse.
Safety and common adverse effects
Abdominal cramping and diarrhoea are predictable adverse effects of excessive or poorly tolerated stimulant-laxative action. Urine colour can also change with anthranoid metabolites and this is not automatically evidence of kidney injury.
The NHS advises that senna is ideally used only for a few days unless it has been prescribed for longer-term use. Prolonged use can contribute to electrolyte imbalance and may impair normal bowel function.[2][3]
Electrolytes and why long-term misuse matters
Repeated diarrhoea can cause clinically important losses of water and electrolytes, particularly potassium. Severe electrolyte disturbance can produce weakness, muscle symptoms, cardiac problems or seizures.
This is where a secondary medicine interaction can arise: hypokalaemia can increase the toxicity risk of medicines such as digoxin and can be particularly problematic alongside other medicines that lower potassium.
When senna is inappropriate
Stimulant laxatives should not be used to self-treat unexplained severe abdominal pain, suspected intestinal obstruction, significant dehydration or an acute abdomen. Persistent constipation, rectal bleeding, unexplained weight loss, vomiting or a major change in bowel habit warrants medical assessment.
Melanosis coli
Long-term exposure to anthranoid laxatives is associated with melanosis coli (also called pseudomelanosis coli), a pigmentation of the colonic mucosa caused by pigment-laden macrophages. It is usually discovered during colonoscopy. Its presence is a marker of chronic anthranoid exposure rather than proof by itself of malignant disease.[6]
Pregnancy, breastfeeding and children
Suitability depends on age, clinical context and the current medicinal-product information. A laxative should not be chosen in pregnancy, breastfeeding or childhood simply because it is plant-derived. Where constipation is persistent or complicated, individual clinical advice is appropriate.
Student note: common evidence traps
- Senna is a stimulant laxative, not a “detoxifying herb”.
- Do not confuse senna leaf with senna pod without checking the preparation.
- Sennosides are converted by gut bacteria; rhein anthrone is a key active colonic metabolite.
- Short-term efficacy does not justify unsupervised chronic use.
- Electrolyte disturbance can create clinically important secondary drug risks.
- Do not describe melanosis coli as synonymous with bowel cancer.
- A laxative-induced weight change is not evidence of fat loss.
References
- European Medicines Agency, Committee on Herbal Medicinal Products. Sennae folium — Senna alexandrina Mill. (Cassia senna L.; Cassia angustifolia Vahl), folium. EU herbal monograph and assessment report, Revision 1. EMA. Final monograph published 2 April 2020; assessment-report addendum published 13 April 2022.
- NHS. Side effects of senna. Includes long-term electrolyte and bowel-function cautions. NHS. Consulted September 2026.
- NHS. Common questions about senna. Mechanism, expected onset and short-term-use guidance. NHS. Consulted September 2026.
- European Medicines Agency, Committee on Herbal Medicinal Products. Sennae fructus — Senna alexandrina Mill., fructus. EU herbal monograph and assessment report. EMA. Revision 1 published 2020; addendum published 2022.
- Lemli J. Mechanism of action of sennosides. Bulletin de l'Académie Nationale de Médecine. 1995;179(8):1605–1611. PubMed.
- de Witte P. Metabolism and pharmacokinetics of anthranoids. Pharmacology. 1993;47 Suppl 1. PubMed.
- Ulbricht C, et al. An evidence-based systematic review of senna (Cassia senna) by the Natural Standard Research Collaboration. Journal of Dietary Supplements. 2011;8(2):189–238. doi:10.3109/19390211.2011.573186. PubMed.
Additional materia medica sources
- ESCOP. Sennae folium and Sennae fructus, ESCOP Monographs.
- British Herbal Medicine Association. British Herbal Compendium, Volume 1 — Senna Leaf and Senna Fruit.
- Blumenthal M, et al., eds. The Complete German Commission E Monographs. American Botanical Council; 1998.
- Hoffmann D. Medical Herbalism. Healing Arts Press; 2003.
Last reviewed: 20 September 2026. Educational reference only; not an individual laxative-treatment or prescribing guide.
← Return to the Herbal Monograph Library | Herbal Medicine Safety and Interactions