Educational information, not medical advice — ask your doctor or midwife.
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Bokusho is a mineral, not a plant. It is purified sodium sulfate (mirabilite, also called Glauber's salt), used in Kampo as a single drug and as an ingredient in several classic formulas. Its job is simple and physical: it pulls water into the bowel so that hard, dry stool softens and moves.
In Kampo it is reached for in short bursts for stubborn constipation with a hard, full, tender belly, and as one part of "purging" formulas such as Daijokito and Tsudosan. Outside Japan the same mineral has a long life in Chinese medicine as Mang Xiao and in old European pharmacy as Glauber's salt.
On the evidence: sodium sulfate is a well-understood osmotic (water-drawing) laxative, and that mechanism is not in doubt. What is thin is trial evidence on Bokusho itself, as a Kampo drug at Kampo doses. Traditional standing and proven effect are two different things, and throughout this page we report them separately.
Bokusho works by osmosis, which means it holds water. Sulfate is poorly absorbed from the gut, so it stays in the bowel and drags water in with it.
That extra water softens hard stool and stretches the bowel wall. The stretch triggers the normal squeezing movement that pushes stool out. This is the same principle behind modern sodium sulfate bowel-prep drinks.
In Kampo theory it is described as softening hardness and draining heat from the interior, which is why it is paired with rhubarb root (Daio) in purging formulas. That is a traditional description of the effect, not a tested biological mechanism.
Bokusho comes in a small number of forms:
- Loose crystals or white powder, dissolved in warm water or in a finished decoction (a strained herbal tea). - A component of Kampo granule and tablet formulas, such as Daijokito, Choijokito, Tsudosan and Bofutsushosan. - Occasionally as an external compress, dissolved in water and applied to the skin, in some traditional practice.
One practical point: Bokusho is not boiled with the other herbs. It is stirred into the hot, finished decoction so it dissolves, because heat and long boiling are not needed and can change the mineral.
Mirabilite appears in the earliest Chinese materia medica and travelled into Japanese Kampo with the Shang Han Lun tradition of formulas, which Kampo practitioners have used since roughly the 16th century onward. It sits inside the classical "purging" formulas rather than being taken alone.
The same mineral was named Glauber's salt in 17th-century Europe after the chemist who described it, and was a standard purgative in Western pharmacy for centuries. So it is one of the few substances with a genuinely cross-cultural record.
Some reactions to Bokusho need urgent care. Call your local emergency number or go to an emergency department straight away — do not wait to see whether it passes.
See a doctor promptly if your constipation lasts more than a week, keeps coming back, or started for no clear reason after the age of 50.
Also get checked if you see blood in your stool, are losing weight without trying, or your stool has changed shape or pattern and stayed changed.
Go to an emergency department, or call emergency services, if you get severe or worsening belly pain, a swollen hard belly with vomiting and no wind passing, or if you become very weak, confused, faint, or notice your heart racing or skipping after taking it. Those can mean a blocked bowel or a serious salt and water imbalance.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
Reviewed by the HealisticMD editorial team How we grade evidence →
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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