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Moderate evidenceGut health

Senna

Senna is a genuinely effective stimulant laxative — it reliably produces a bowel movement within 6-12 hours and is a first-line option for opioid-induced constipation. It is for short-term or supervised use, not for daily "detox teas," and chronic misuse causes electrolyte loss and dependence-like patterns.

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What the science says

  • Relieves chronic constipation Moderate evidence

    A 2023 systematic review and meta-analysis of food and supplement interventions for chronic constipation in adults found senna among the agents improving stool frequency and consistency, though the pooled estimates rested on a small number of randomized trials. Decades of clinical use and regulatory approval as an OTC laxative back its short-term efficacy; what is weak is evidence for long-term daily use.

  • Treats and prevents opioid-induced constipation Moderate evidence

    A 2024 systematic review and meta-analysis of opioid-induced constipation in cancer patients supports stimulant laxatives including senna as standard prophylaxis alongside opioid initiation, with efficacy broadly comparable to osmotic agents such as polyethylene glycol. Palliative-care guidelines recommend starting a stimulant laxative with every opioid prescription.

  • Causes weight loss ("detox" and slimming teas) Limited evidence

    Any weight change from senna is water and stool weight, recovered within a day or two; it acts in the colon, downstream of where calories are absorbed, so it does not reduce fat mass or energy uptake. Slimming-tea use is a recognized pathway into laxative misuse and hypokalemia.

  • Bowel preparation before colonoscopy Moderate evidence

    Network meta-analyses of bowel preparation regimens find senna-containing and senna-augmented regimens achieve adequate cleansing, generally as an adjunct to polyethylene glycol rather than as a standalone. Regimen choice should follow the endoscopy unit's protocol.

Dosage & safety

Studied doseStandard adult dose is 15-30 mg of sennosides at bedtime (typically 1-2 tablets), producing a bowel movement in 6-12 hours; palliative-care regimens titrate up to about 100 mg/day of sennosides. Children's doses are weight-based and should be set by a clinician. Do not use continuously for more than 1-2 weeks without medical supervision.
SafetyExpect abdominal cramping, urgency and diarrhea; overuse causes dehydration, hypokalemia and hypomagnesaemia. Prolonged use produces melanosis coli (a benign, reversible pigmentation) and, in chronic abusers, electrolyte disturbance and possible colonic dysmotility. Rare hepatotoxicity has been reported with chronic high-dose use. Potassium loss increases digoxin toxicity risk and compounds thiazide/loop diuretics and corticosteroids. Contraindicated in bowel obstruction, ileus, acute inflammatory bowel disease, appendicitis, undiagnosed abdominal pain and severe dehydration. Avoid in pregnancy except on medical advice; small amounts enter breast milk. Regulatory note: the EU banned aloe-emodin, emodin and danthron and preparations containing them in food supplements in 2021 and restricts hydroxyanthracene derivatives generally, while senna leaf/pod preparations remain available as licensed OTC medicines in most markets with mandatory short-duration labelling.

How to take it

TimingAt bedtime — it works in 6-12 hours, so the effect arrives in the morning.
With food?With or without food.
Worth knowingIf you need it beyond a couple of weeks, the problem is not laxative supply — get the constipation properly assessed rather than escalating the dose.

Interactions

With medications

  • digoxin

    Potassium loss from repeated use increases digoxin toxicity risk. do not use regularly on digoxin without medical supervision

  • thiazide and loop diuretics, and corticosteroids

    Additive potassium and magnesium loss. limit to short courses and have electrolytes checked if used longer

  • all oral medications

    Accelerated bowel transit reduces the time available for drugs to be absorbed. separate by at least 2 hours where the drug matters

With other supplements

  • aloe latex, cascara and other stimulant laxatives

    Additive cramping, dehydration and potassium loss. do not combine

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

How long does senna take to work?

Senna usually produces a bowel movement within 6-12 hours, so it is taken at bedtime. The standard adult dose is 15-30 mg of sennosides.

Is it safe to take senna every day?

Senna is for short-term use: do not use it continuously for more than 1-2 weeks without medical supervision. Chronic overuse causes dehydration, low potassium and magnesium, and possible colonic dysmotility.

Does senna tea help you lose weight?

No. Any weight lost with senna is water and stool, regained within a day or two, because senna acts in the colon after calories are absorbed. Slimming-tea use is a recognised path into laxative misuse.

Is senna good for opioid-induced constipation?

Yes — senna has moderate evidence as standard prevention for opioid-induced constipation, broadly comparable to polyethylene glycol, and palliative-care guidelines recommend starting a stimulant laxative with every opioid prescription.

Scientific references

Where to buy

NOW Foods, Senna Leaves, 470 mg, 100 Veg Capsules

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