What is Deng Xin Cao?

Deng Xin Cao is the dried white pith inside the stem of a rush plant. The plant is Juncus effusus, a marsh reed. In English it is often called rush pith or juncus.

It is one single herb, not a mix. Chinese medicine uses it as a mild, light tea. The main uses are to calm a restless mind, help sleep, and help you pass more urine.

Here is the short verdict on proof. It has a long record of use in one tradition, but we found no human trials of it. A long history of use is not proof that a herb works.

How does Deng Xin Cao work?

No one has shown how it works in people. In Chinese medicine it is said to clear heart fire and to drain damp heat out through the urine. Those are old ways of saying what it is used for, not a tested answer.

Lab work points to a few plant compounds that calm mice. The pith is mostly air and fibre, so a tea made from it is weak. Any effect in a person is likely to be small.

What forms does Deng Xin Cao come in?

You will most often see loose strands of dried white pith for tea. It is very light, so even a small dose looks like a big pile. Powder and ready-made granules are also sold.

Two special forms exist. Charred pith, called Deng Xin Tan, was used in the past for bleeding. Cinnabar-coated pith carries mercury and is not safe to take.

It is rarely used on its own. Most of the time it is one small part of a larger formula. The same pith was once used as a lamp wick, which is where the name comes from.

Where it comes from:

Deng Xin Cao means lamp wick grass. Chinese doctors have used it for many hundreds of years, with records going back to about the Song era. Later herb books list it as a gentle herb for fussy children and for hot, scanty urine.

What does Deng Xin Cao help with?

• Trouble falling asleep and night restlessness: This is the best known use in Chinese medicine, where the herb is added to a formula to settle a hot, restless mind. We found no human trials of Deng Xin Cao for sleep. Mouse studies of single rush compounds show some calming, which does not tell you what a weak tea does in a person.
• Night crying and fussiness in children: Old Chinese texts use tiny amounts of the pith for babies and small children who cry at night. There is no trial evidence at all for this use. Do not give it to a child without advice from a qualified practitioner, and see a doctor if a child has fever or seems unwell.
• Mouth and tongue sores: Tradition treats mouth sores as heat in the heart channel, and this herb is one of the mild options used. No human study has tested it for mouth sores. Most mouth ulcers heal on their own within two weeks.
• Hot, scanty or painful urine: The herb is classed in Chinese medicine as one that helps you pass more urine. Burning or painful urine is often a urine infection, which needs proper testing and may need antibiotics. There is no trial evidence that this herb treats any infection.
• Mild swelling from fluid build-up: Traditional texts list it for mild puffiness alongside stronger herbs. There is no human evidence for this. New or growing swelling of the legs, face or belly needs a doctor, as it can come from the heart, kidneys or liver.
• Sore, hot throat: It appears in some throat formulas as a cooling, minor ingredient. No trials support this. A sore throat with high fever, drooling or trouble breathing is an emergency.

Which foods are rich in Deng Xin Cao?

Deng Xin Cao is a medicinal herb, not a food, and it is not part of any normal diet.

What are the side effects of Deng Xin Cao?

• Passing urine more often
• Mild stomach upset
• Dry mouth or thirst
• Light-headedness if you are low on fluid
• Rash or itch, rarely, in people allergic to grasses and rushes
• Mercury poisoning from cinnabar-coated products, which is serious

Good to know:

Plain rush pith is thought of as a very mild herb, and reports of harm from it are rare. The real risk sits with the product, not the plant: cinnabar-coated pith contains mercury, and poorly controlled herb supplies can carry other heavy metals or the wrong plant. Buy only tested, clearly labelled herb from a trusted supplier.

How much Deng Xin Cao should you take?

• Recommended daily: No modern tested dose exists. In Chinese practice the usual amount is about 1 to 3 grams of dried pith a day, simmered in water. Children are given much less, and only on a practitioner's advice.
• Best time of day: For sleep or restlessness, people usually drink it in the evening. For urinary complaints it is taken during the day, so you are not up all night passing urine.
• With or without food: Either. Taking it between meals is common; take it with food if plain tea upsets your stomach.
• Time to effect: Unknown. Traditional use suggests any calming effect would be felt the same evening, but no study has measured this.
• How long to take it: It is normally used for a short run of a few days to about two weeks, then stopped. If nothing has changed after two weeks, stop and get your symptoms checked.