Educational information, not medical advice — ask your doctor or midwife.
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San Leng is the dried rhizome (underground stem) of the marsh plant Sparganium stoloniferum. In Traditional Chinese Medicine it is a single herb used to "break blood stasis" and move qi. Practitioners give it for fixed lumps in the belly, painful periods and old, stubborn swellings.
It is rarely used alone. It is nearly always paired with E Zhu (Curcuma rhizome) inside a larger formula. The raw herb is often processed with vinegar before use.
The honest evidence verdict is simple. Its record in Chinese medicine is long and well documented. Human trials of San Leng by itself are essentially absent, and traditional use is not proof that it works.
No one has shown in people how San Leng works, or that it works at all.
In TCM theory, it is a strong "blood-moving" herb. It is said to break up stasis, soften hard masses and ease the pain that comes with them. That is a traditional model, not a biological one.
Laboratory work gives some clues. In test tubes and in animals, extracts appear to slow blood clotting and reduce the clumping of platelets (the cells that plug a wound). Cell studies also report effects on the growth of some tumour cell lines.
Whether any of this happens in a person who drinks a decoction is not known. The blood-thinning signal matters anyway, because it lines up with the traditional warnings about bleeding.
San Leng reaches most people as part of a prescribed formula, not as a standalone product.
Common forms: - Dried sliced rhizome, for boiling into a decoction (a strong tea) - Vinegar-processed slices, the usual form for pain and stasis patterns - Granules or a powdered extract, dissolved in hot water - Pills or capsules within a patent Chinese formula
Tinctures and Western-style single-herb capsules exist but are uncommon.
San Leng has been in Chinese materia medica for well over a thousand years. It appears in Tang and Song dynasty texts, including the Ri Hua Zi Ben Cao, and stays in mainstream use today.
It has always been classed as a strong, driving herb. Classical writers warned against long use, and against use in weak patients. It is not used in the herbal traditions of India, Europe or the Americas.
See a doctor straight away if you bleed and cannot stop it, pass black or tarry stools, vomit blood, or bruise for no clear reason.
See a doctor soon if your periods become much heavier or last longer than usual while taking it. Stop the herb first.
Get checked before starting if you have a lump in your belly, a missed period, or pain that is new or getting worse. A cause needs to be found first.
Speak to your doctor or pharmacist before you start if you take any prescription medicine at all.
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 →
The published evidence for San Leng is weak or absent. That usually means no controlled trial has tested it, not that a trial found it ineffective — the two are different, and we grade only what has been published.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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