What is Ya Zhi Cao?

Ya Zhi Cao is the dried above-ground part of the Asiatic dayflower (Commelina communis), a common blue-flowered weed. It is used in Chinese herbal medicine as a single herb to cool fevers, ease a hot sore throat, and help the body pass more urine.

Practitioners use it for short, sharp problems rather than long-term ones. Typical uses are a feverish cold, a red painful throat, or puffiness and difficult urination. Fresh crushed leaves have also been laid on boils, insect bites and snake bites in folk practice.

Here is the honest verdict. Ya Zhi Cao has a recognised place in classical Chinese formularies, but published human trials are essentially absent, so we cannot say what it does in people. Traditional use tells you a plant has been trusted for a long time; it is not proof that it works, and that applies to everything described on this page.

How does Ya Zhi Cao work?

In Chinese medicine terms, Ya Zhi Cao is described as cold and sweet-bland. It is said to clear heat, resolve toxin, and drain water downward through urination. Those are traditional descriptions of what the herb does, not measurements of what happens in the body.

Laboratory and animal studies suggest a few possible actions. Extracts have increased urine output in animals, reduced markers of inflammation (swelling and irritation) in test systems, and slowed the digestion of starch in the gut.

None of this has been confirmed in people. Treat any mechanism you read about Ya Zhi Cao, including the ones above, as an unproven idea rather than a settled fact.

What forms does Ya Zhi Cao come in?

Ya Zhi Cao is nearly always used as a water decoction, meaning the dried herb is simmered in water and the liquid is drunk. This is the form Chinese herbalists use most.

You may also meet it as loose dried herb sold by weight, as granules or powder made from a concentrated water extract, or as fresh herb.

Fresh crushed herb is applied to the skin in folk practice for bites and boils. It is occasionally one ingredient in a multi-herb formula rather than a stand-alone remedy. Standardised capsules and tinctures are uncommon in Western shops.

Where it comes from:

Ya Zhi Cao appears in Chinese materia medica writings from around the Tang dynasty onward and is listed in modern Chinese pharmacopoeial texts as a heat-clearing, toxin-resolving herb. The plant is also eaten as a wild green and used in folk remedies in Japan and Korea. Its standing is solid within Chinese practice but it is a secondary, everyday herb rather than a famous one.

What does Ya Zhi Cao help with?

• Fever during a cold or flu: This is the main traditional use. Chinese texts group Ya Zhi Cao with herbs that cool a feverish body and are given for a few days at the start of an illness. No published human trial has tested whether it shortens a fever or a cold.
• Hot, red sore throat: Traditionally used alone or with other cooling herbs for a throat that feels hot and raw. The evidence here is entirely traditional. If a sore throat comes with a high fever, trouble swallowing or trouble breathing, that needs a doctor, not a herb.
• Painful or difficult urination: Chinese practice uses Ya Zhi Cao to promote urine flow when passing water is scanty or burning. Animal studies do show increased urine output. Human evidence is absent, and burning urination often means a urine infection that needs proper treatment.
• Swelling from fluid build-up (oedema): Used traditionally for puffiness in the face, legs or ankles, on the reasoning that the herb drains water downward. New or one-sided swelling can signal heart, kidney or liver problems, so get it checked before treating it yourself.
• Boils, insect bites and snake bites, applied to the skin: Folk practice crushes the fresh plant and lays it on the spot. This is a long-standing custom with no clinical testing behind it. A snake bite is a medical emergency and needs a hospital, never a plant poultice alone.

Which foods are rich in Ya Zhi Cao?

1. Young dayflower shoots and leaves: eaten as a cooked wild green in parts of Japan, Korea and China
2. Dayflower leaf tea: a folk drink made from the same plant

Practical Tips:

Food amounts of the young shoots are small and mild; medicinal decoctions are far stronger.

What are the side effects of Ya Zhi Cao?

• Passing urine more often
• Loose stools or diarrhoea
• Stomach ache or cramping
• Feeling cold, tired or washed out, especially with longer use
• Low blood sugar signs such as shakiness, sweating or confusion, if you also take diabetes medicine
• Skin rash or itching, rarely, from an allergy

Good to know:

Ya Zhi Cao is generally regarded as gentle at traditional doses, and serious harm has not been reported in the literature. The common complaints are digestive: loose stools and cramps, which reflect the herb's cold, draining nature.

Because reporting on this plant is thin, absence of reports is not the same as proof of safety. Stop taking it if anything new and unpleasant starts.

How much Ya Zhi Cao should you take?

• Recommended daily: There is no dose established by research. The amounts below come from Chinese herbal practice, not from trials. Typical decoction dose is 9 to 30 grams of dried herb per day, simmered in water and drunk in two or three portions. Fresh herb is used at higher weights, often 60 to 90 grams. Granules and powders should be dosed by the maker's label, since they are concentrated.
• Best time of day: Split the daily amount into two or three doses spread through the day. Because it makes you pass more urine, take the last dose well before bedtime.
• With or without food: Usually taken warm, between meals. If it upsets your stomach, take it with food instead.
• Time to effect: Traditionally it is expected to act within hours to a couple of days when it is going to help at all. There is no trial evidence to confirm any time frame.
• How long to take it: This is a short-term herb. Chinese practice uses it for a few days up to about a week, for a problem that is here now. If your fever, throat or urinary symptoms have not clearly improved in three days, stop and see a doctor rather than continuing.