Senna: what it treats, how to take it, side effects
Last updated September 3, 2026.
Senna is a stimulant laxative - it increases activity in the intestines to produce a bowel movement. You may know it as Senokot or Ex-Lax. It is the reliable overnight option, and the "short-term" in its instructions is the part people skip.
What does it treat?
Constipation, on a short-term basis - and bowel emptying before surgery and certain medical procedures. It works on a 6-to-12-hour clock, which is why bedtime dosing produces a morning result.
How do you take it?
Once or twice daily, as the package or prescription directs - bedtime is the classic slot. Swallow the coated tablets (Ex-Lax, Perdiem Overnight Relief) whole with a glass of water; no splitting or chewing. The hard rule: do not take senna for more than 1 week without talking to your doctor, and do not take more if a regular movement has not happened - that is a doctor conversation, not a bigger dose. Frequent or continued use can create laxative dependence and let the bowels lose their normal activity. Certain products (Ex-Lax, Perdiem) go at least 2 hours before or after other oral medications. It is usually taken as needed, so a missed dose only matters on a prescribed schedule: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: stomach discomfort or cramps, nausea, faintness, and brown-discolored urine - harmless but surprising if nobody warned you.
- Serious - stop taking it and call your doctor immediately: rectal bleeding.
Who should not take it?
Anyone with stomach pain, nausea, vomiting, or a sudden change in bowel habits lasting more than 2 weeks needs a doctor before a laxative, not after. Mineral oil interacts with it. Older adults should not use senna long-term - safer maintenance options exist. And the base layer MedlinePlus emphasizes: a high-fiber diet, plenty of liquids, and exercise are the actual long-term bowel program; senna is the bridge, not the road. If you become pregnant, call your doctor.
When is it an emergency?
Rectal bleeding means stop and call immediately. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why can't I just take senna every day for constipation?
Dependence. MedlinePlus warns that frequent or continued use can make you dependent on laxatives and cause your bowels to lose their normal activity - the gut learns to wait for the stimulant. The label rule is no more than 1 week without your doctor. Constipation that needs a daily laxative needs a diagnosis, and fiber, fluids, and exercise are the actual maintenance plan.
Why take senna at bedtime?
Its working clock is 6 to 12 hours - MedlinePlus notes it may be taken at bedtime to produce a bowel movement the next day. Night dosing lines the effect up with morning routine, which is when most people want it. Daytime dosing works the same way, just shifted.
Why is my urine brown on senna?
A known, harmless effect on the common-effects list: senna can discolor urine brown. It is the drug's pigments clearing, not blood, and it reverses when you stop. The color that does matter is red - rectal bleeding is the stop-and-call effect.
Why do I have to separate senna from my other pills?
Some senna products can affect how other medications work. MedlinePlus says to take Ex-Lax and Perdiem Overnight Relief at least 2 hours before or after other oral medications. A faster-moving gut gives other drugs less time to absorb - the 2-hour buffer protects them.
Is senna natural and therefore safer?
It is plant-derived, and it is still a drug with rules: a 1-week limit, a dependence risk, an age caution for long-term use in older adults, and a bleeding stop sign. Natural origin changes the marketing, not the pharmacology. Short-term, as directed, it is a well-understood tool.
What happens if senna doesn't work?
Stop and call your doctor - MedlinePlus says that directly: if you do not have a regular bowel movement after taking senna, do not take more of it. No result is information: it can mean a blockage or another condition that laxatives make worse, not better.