Senna is a natural stimulant laxative derived from the Cassia plant. It is a common over-the-counter solution for occasional constipation.
Onset of Action
Senna produces a bowel movement within 6 to 12 hours. This delayed effect means it is not an immediate solution for constipation. Many individuals find it effective to take senna at bedtime, allowing the medication to work overnight for a bowel movement the following morning.
Individual metabolic rates and digestive systems influence the exact timing. While tablets fall within the 6-12 hour window, liquid formulations, especially on an empty stomach, might act faster, within 1 to 3 hours.
How Senna Works
Senna’s laxative properties stem from active compounds known as sennosides. When ingested, these sennosides remain largely inactive as they pass through the stomach and small intestine. Their transformation into an active form occurs in the large intestine.
Once in the colon, gut bacteria metabolize the sennosides into their active metabolite, rhein anthrone. This active compound then exerts its effect through a dual mechanism. Rhein anthrone stimulates the smooth muscle cells lining the colon, increasing peristalsis—the rhythmic contractions that propel fecal matter. This enhanced motility accelerates the transit of stool, reducing the time available for water reabsorption.
Rhein anthrone also influences the balance of electrolytes and water in the colon. It works by inhibiting the absorption of water and sodium ions, while promoting the secretion of water and electrolytes into the colon. This influx of water into the intestines softens the stool, making it easier to pass.
Important Considerations for Use
When using senna, following the product’s specific dosage instructions is important. General guidelines for adults suggest taking one to two tablets, or one to two 5ml of syrup, at bedtime. The maximum daily dose can vary by formulation but does not exceed four tablets.
Maintaining adequate hydration is also important while taking senna; drinking six to eight glasses of fluids daily can help prevent constipation from worsening. Senna is intended for short-term use, no longer than seven days. Prolonged use beyond seven days can lead to dependency, where the bowels may lose their natural ability to function independently, and may also result in electrolyte imbalances, particularly low potassium levels.
While well-tolerated, some mild side effects can occur, including abdominal cramping, nausea, diarrhea, and gas. These effects are temporary. A harmless reddish-brown discoloration of the urine may also be observed.
When to Seek Medical Advice
Consulting a healthcare professional is advisable if constipation does not improve after one week of using senna. Medical attention is also warranted for severe or persistent abdominal pain, nausea, or vomiting. The presence of blood in the stool or rectal bleeding requires immediate medical evaluation.
If senna fails to produce a bowel movement within the expected 6 to 12 hours, or after three days of use, seek advice. Unusual or severe side effects, such as muscle cramps, weakness, irregular heartbeat, dizziness, decreased urination, or confusion, warrant medical consultation. Any sudden change in bowel habits that persists for more than two weeks warrants professional guidance.