Recommended Dosage of Senna
For adults and children over 12 years, start with 8.6-17.2 mg of sennosides daily, taken at bedtime, and titrate upward based on response; the recommended maximum is 4 tablets twice daily (approximately 34.4-68.8 mg/day). 1
Adult Dosing (≥12 years)
- Initial dose: 8.6-17.2 mg sennosides daily (equivalent to 1-2 standard tablets containing 8.6 mg each)
- Timing: Take at bedtime for overnight effect
- Titration: Increase dose gradually if no response after several days
- Maximum dose: 4 tablets twice daily (no clear absolute maximum, but this represents practical upper limit) 1
FDA-Approved Liquid Formulation Dosing
For senna syrup (8.8 mg/5 mL):
- Usual dose: 2-3 teaspoons (10-15 mL) once daily
- Maximum dose: 3 teaspoons (15 mL) twice daily 2
Pediatric Dosing (6-12 years)
For liquid formulation (8.8 mg/5 mL):
- Usual dose: 1 to 1.5 teaspoons (5-7.5 mL) once daily
- Maximum dose: 1.5 teaspoons (7.5 mL) twice daily 2
Critical Implementation Points
Start low and go slow. The 2023 AGA-ACG guidelines explicitly note that trial doses (1 g daily, equivalent to ~115 mg sennosides) were substantially higher than typical clinical practice, and 83% of trial participants reduced their dose due to side effects 1. Most commercially available tablets contain 8-9 mg sennosides per tablet 1.
Common pitfalls to avoid:
- Abdominal cramping and diarrhea are dose-dependent; these occur more frequently at higher doses and typically in the first week of treatment 1
- Perineal blistering can occur with high doses combined with prolonged stool-to-skin contact, particularly with nighttime accidents—advise frequent diaper changes in non-toilet-trained children 3
- Antibiotic interference: Concurrent antibiotic use may reduce senna efficacy since gut bacteria are required to convert sennosides to active metabolites 1
Mechanism and Onset
Senna works as a stimulant laxative—sennosides A and B are metabolized by gut bacteria into active compounds (rheinanthrone and rhein) that stimulate prostaglandin E2 production, increase chloride secretion, and enhance colonic peristalsis 1. Onset of action is typically 6-12 hours, making bedtime dosing optimal for morning bowel movements.
Duration of Therapy
While clinical trials evaluated 4-week treatment periods, longer-term use is likely appropriate for chronic idiopathic constipation, though rigorous long-term safety data are lacking 1. The guidelines suggest senna can be used as first-line therapy given its efficacy, low cost (<$50/month), over-the-counter availability, and impact on quality of life 1.
Contraindications
Do not use senna in patients with:
- Intestinal obstruction or ileus
- Severe dehydration
- Acute inflammatory bowel conditions
- Pregnancy (due to potential weak genotoxic effects, though evidence is controversial) 1