The herbal supplement senna, derived from the leaves and fruit of the Senna alexandrina plant, is a widely recognized stimulant laxative. While a complex array of natural chemicals exists within the plant, its purgative action is almost entirely attributable to a specific group of compounds. Understanding the composition of senna reveals why it is an effective, yet potent, natural remedy. The main compounds present are called sennosides.
The Dominant Players: Sennosides A and B
At the heart of senna's laxative power lie the sennosides, a group of dimeric anthraquinone glycosides. Among these, sennosides A and B are the most abundant and potent. These molecules are not absorbed in the upper gastrointestinal tract but instead travel to the large intestine where they can exert their effects. As stimulant laxatives, their mechanism is distinct from other laxative types, which is why users often feel its effects within a predictable timeframe. It is crucial to recognize these specific compounds as the key to its action.
How Sennosides Work in the Body
When senna is ingested, the sennosides remain in their inactive state until they reach the colon. Here, resident bacteria break down the sennosides through a process called hydrolysis. This process releases the active compounds, known as anthrones, into the colon. These anthrones then act as local irritants, performing two primary functions to promote a bowel movement:
- They directly stimulate the intestinal mucosa and nerve plexuses, causing increased muscle contractions (peristalsis) that move stool through the colon more quickly.
- They alter water and electrolyte secretion, inhibiting the reabsorption of fluids and increasing the water content of the stool. This results in a softer, bulkier stool that is easier to pass.
This two-pronged mechanism explains why senna is considered such a powerful and fast-acting laxative, typically producing effects within 6 to 12 hours. The delayed onset is a direct result of waiting for the sennosides to reach the colon and be metabolized.
Beyond Sennosides: Other Constituents
While sennosides are the most active components, senna contains a cocktail of other phytochemicals that contribute to the plant's overall composition. These include smaller amounts of other anthraquinone glycosides (like sennosides C and D), as well as free anthraquinones such as rhein, aloe-emodin, and chrysophanol. The plant also contains flavonoids like isorhamnetin and kaempferol, mucilage, and phytosterols. Some of these compounds, particularly rhein, may possess other protective effects, including anti-inflammatory and hepatoprotective properties. However, the laxative effect is primarily attributed to the sennosides and their metabolites.
Comparison of Senna Species and Preparations
Different species and parts of the senna plant can have varying concentrations of sennosides, impacting their potency. For commercial and medicinal purposes, the two most common species are Cassia angustifolia (Indian or Tinnevelly senna) and Cassia acutifolia (Alexandrian senna).
| Feature | Indian Senna (C. angustifolia) | Alexandrian Senna (C. acutifolia) |
|---|---|---|
| Origin | Mainly cultivated in India | Wild-grown in Africa, particularly Egypt and Sudan |
| Sennoside Content | Contains anthraquinone glycosides like sennosides A and B, and is standardized to not less than 2.0% anthracene derivatives. | Contains anthraquinone glycosides, including sennosides A and B. |
| Potency | Considered a reliable purgative, similar in action to the Alexandrian variety. | Also a powerful purgative and standardized in many pharmacopoeias. |
| Common Forms | Dried leaflets and pods. | Leaves and pods, with pods often perceived as gentler. |
| Appearance | Yellowish-green, elongated leaflets with pointed apex. | Native to North Africa, used since the 9th century by Arabian physicians. |
It is also noted that the pods of the senna plant tend to have a gentler effect than the leaves. The American Herbal Products Association (AHPA) recommends labeling for senna leaf products to indicate they are not for long-term use, while not applying the same warning to fruit-based products. This difference is largely due to the varying concentrations of sennosides in the plant parts.
Risks and Safe Usage of Senna
While effective, senna is a powerful laxative and should be used with caution. It is only intended for short-term relief of constipation, typically for no more than one week unless otherwise advised by a healthcare provider. Prolonged use can lead to serious health complications, including:
- Laxative Dependency: Chronic use can cause the bowels to become dependent on the stimulant, leading to poor bowel function on their own.
- Electrolyte Imbalance: The mechanism of action, which involves inhibiting electrolyte absorption, can lead to critically low levels of potassium in the body. This can affect heart function, cause muscle weakness, and other harmful effects.
- Abdominal Discomfort: Side effects such as stomach cramps, discomfort, and diarrhea are common, particularly with higher doses.
- Liver Damage: Although rare, liver injury has been reported in cases of prolonged, high-dose senna use.
Individuals should also be aware of potential drug interactions, especially with diuretics, blood thinners (like warfarin), and certain heart medications (like digoxin).
Conclusion
In summary, the potent laxative action of senna is primarily due to its content of sennosides, particularly sennosides A and B. These anthraquinone glycosides are activated by gut bacteria in the colon, where they stimulate bowel contractions and increase stool water content. While highly effective for short-term constipation, understanding what senna mainly contains and its powerful mechanism is vital for safe and responsible use. Its potent nature underscores the importance of adhering to recommended dosages and avoiding prolonged use to prevent serious health risks.
Read more about Senna's laxative properties and usage on WebMD
