What is senna?: A comprehensive guide to the herbal laxative

October 6, 2025 •

4 min read

Used for centuries by Arabian physicians in the 9th century, senna is a powerful herbal laxative derived from the leaves and fruit of the Cassia plant species. Today, it is an FDA-approved nonprescription medication for the short-term treatment of occasional constipation, valued for its effectiveness and predictable action.

Quick Summary

Senna is an herbal stimulant laxative derived from the Cassia plant, used for the short-term treatment of constipation. It works by stimulating intestinal muscles via active compounds called sennosides, promoting a bowel movement typically within 6 to 12 hours. It is available over-the-counter in various forms and is intended for occasional, not long-term, use.

Key Points

Source: Senna is an herbal medicine derived from the leaves and fruits of the Cassia plant, specifically Cassia senna or Cassia angustifolia.
Mechanism of Action: It is a stimulant laxative, utilizing active compounds called sennosides that stimulate intestinal muscles and increase intestinal fluid to promote a bowel movement.
Primary Use: Senna is approved for the short-term treatment of occasional constipation and for bowel cleansing before certain medical procedures.
Important Warning: Long-term or excessive use is strongly discouraged due to risks of laxative dependence, electrolyte imbalance, and potential harm to the colon.
Common Side Effects: The most frequent side effects include abdominal cramps, discomfort, and diarrhea, as well as a harmless discoloration of the urine.
Drug Interactions: Senna can interact with other medications, particularly diuretics, digoxin, and warfarin, and caution is advised.
Comparison: Unlike bulk-forming or osmotic laxatives, senna works more quickly but is not intended for long-term management of constipation.

What is senna and where does it come from?

Senna is an herbal medicine produced from the dried leaves and fruits of the Cassia senna and Cassia angustifolia plants, a genus found in tropical regions worldwide. Historically, it has been used in traditional folk medicine for its potent cathartic and stimulant properties. Modern medicine has since standardized the active components, known as sennosides, to ensure consistent and safe use in over-the-counter products. Senna is widely recognized and is the primary active ingredient in several common brand-name laxatives, including Senokot and Ex-Lax.

How does senna work as a laxative?

Senna functions as a stimulant laxative, meaning it increases the activity and contractions of the muscles lining the intestines. The core mechanism involves its active ingredients, the sennosides, which are not absorbed in the small intestine but are instead broken down by colonic bacteria. This process releases active compounds that then act on the colon in two primary ways:

Intestinal Irritation: The active metabolites locally irritate the lining of the colon, which stimulates the intestinal muscles to contract more frequently and with greater force.
Increased Fluid Accumulation: Sennosides and their metabolites also increase the fluid and electrolyte content within the colon by inhibiting water and electrolyte reabsorption. This softens the stool, making it easier to pass.

This two-pronged action results in a bowel movement that typically occurs within 6 to 12 hours after taking the medication. Because of this delay, senna is often recommended to be taken at bedtime to produce an effect the following morning.

Uses for senna

Senna is medically approved for the short-term treatment of occasional constipation. It is also used to help clear the bowels before certain medical procedures, such as a colonoscopy. It is available in several forms, including tablets, capsules, liquids, and teas. Specific instructions on the product label or from a healthcare provider should always be followed. It is crucial to use senna as directed and not to exceed the recommended duration of use, which is typically no more than one week.

List of key precautions for senna use:

Short-Term Use Only: Do not use for more than one week without a doctor's supervision, as long-term use can lead to laxative dependence and other serious side effects.
Stay Hydrated: Drink plenty of fluids to prevent dehydration, a risk associated with diarrhea caused by laxatives.
Check for Medical Conditions: Do not use if you have intestinal blockage, inflammatory bowel disease (Crohn's, ulcerative colitis), appendicitis, or unexplained stomach pain, as senna can worsen these conditions.
Inform Healthcare Providers: Always tell your doctor or pharmacist about any medications or supplements you are taking to check for potential drug interactions, especially with diuretics, digoxin, and warfarin.

Side effects and risks of senna

While generally considered safe for short-term use, senna can cause side effects. The most common side effects are abdominal cramps, discomfort, and diarrhea. These effects are more likely with higher amounts or prolonged use. A harmless side effect is the potential for urine to turn a reddish-brown color, which disappears after discontinuing the medication.

Serious risks associated with improper or long-term use include:

Electrolyte Imbalance: Extended use can disrupt the body's electrolyte balance, particularly potassium levels, which can lead to serious health issues like muscle spasms, irregular heartbeat, or seizures.
Laxative Dependence: Chronic use can cause the bowel to lose its natural function, making it dependent on laxatives for a bowel movement.
Cathartic Colon: Long-term abuse can lead to a condition where the colon's muscles become damaged and unable to function properly.
Liver Damage: In rare cases, especially with high amounts and prolonged use, senna has been linked to liver injury.

Senna vs. other laxatives: A comparison

It is important to understand how senna differs from other types of laxatives to choose the most appropriate treatment for your needs. Different types of laxatives work through various mechanisms, affecting how quickly and gently they relieve constipation.


Feature	Senna (Stimulant)	Psyllium (Bulk-forming)	Lactulose (Osmotic)	Docusate (Stool Softener)
Mechanism	Stimulates intestinal muscles to contract.	Absorbs water to add bulk to stool.	Draws water into the gut to soften stool.	Lets water penetrate and soften stool.
Onset	6–12 hours, typically overnight.	12–72 hours (1–3 days).	At least 2 days.	12–72 hours.
Appropriate Use	Short-term, occasional constipation.	Mild constipation, long-term fiber supplement.	Chronic constipation (often prescribed).	To prevent straining, often after surgery or childbirth.
Common Side Effects	Stomach cramps, diarrhea, urine discoloration.	Bloating, gas, requires ample water.	Stomach pain, gas, cramping.	Stomach cramps, diarrhea.
Long-Term Risk	Laxative dependence, cathartic colon, electrolyte imbalance.	Generally safe, but misuse can cause blockage.	Generally safe under medical supervision.	Rare, but can interact with mineral oil.

Conclusion

What is senna? It is a natural, yet potent, stimulant laxative that is effective for the short-term relief of occasional constipation. Its predictable action and over-the-counter availability make it a common choice for many individuals. However, its use requires careful attention to instructions for use and duration to avoid side effects and more serious health risks associated with long-term misuse, such as electrolyte imbalances and dependency. Before starting any new medication, including herbal remedies like senna, it is essential to consult a healthcare provider to ensure it is the right option for your specific health needs.

For more detailed information on stimulant laxatives and safe usage, consult the U.S. National Library of Medicine's MedlinePlus resource.

Frequently Asked Questions

Senna typically produces a bowel movement within 6 to 12 hours after consumption. For this reason, it is often recommended to be taken at night to provide relief the following morning.

No, senna is not intended for long-term use. The recommended duration is typically no more than one week, as prolonged use can lead to laxative dependence, electrolyte imbalance, and damage to the colon.

If pregnant or breastfeeding, you should consult your healthcare provider before taking senna. Small amounts of senna can pass into breast milk, but it is not typically considered harmful for nursing infants when used as directed for a short time.

Common side effects include stomach cramps, diarrhea, and abdominal pain. A temporary, harmless reddish-brown discoloration of the urine can also occur.

Senna is a stimulant laxative that works more quickly (6-12 hours) by stimulating muscle contractions. Psyllium, a bulk-forming laxative, works more slowly (12-72 hours) by adding fiber and absorbing water to soften stool, and is generally gentler for long-term use.

Since senna is used on an 'as-needed' basis for occasional constipation, you do not need to take a double dose to compensate. Just take the missed dose as soon as you remember, unless it is almost time for your next scheduled dose.

You should stop taking senna and contact a healthcare provider immediately if you experience rectal bleeding, a lack of bowel movement after using the medication, or signs of a serious allergic reaction.