What is Osuyu?

Osuyu is the dried, unripe fruit of a small tree in the citrus family. It is used as a single drug (Korean). The Latin name is Tetradium ruticarpum; it is also known as evodia fruit (Soeumin).

Korean medicine calls it a warming herb. It is given for belly pain that feels cold and eases with heat. It is also used for nausea, vomiting, some headaches, and cold hands and feet.

The human proof is thin. The plant has been used for many centuries in East Asia, but good trials of the fruit on its own are missing. A long history of use is not proof that a herb works.

How does Osuyu work?

No one has shown how Osuyu works in the human body.

Lab work points to two bitter compounds, evodiamine and rutaecarpine. In test tubes they act on TRPV1, a sensor on nerve cells that reacts to heat and chilli. That may be why the fruit tastes hot and why old texts call it warming.

Animal studies suggest it can calm the gut, ease vomiting and change blood flow. Animals are not people. Treat all of this as a clue, not a fact.

One effect is better mapped. Rutaecarpine speeds up CYP1A2, a liver enzyme that clears many drugs. Most of that work is in cells and animals, but it is the main reason to take the drug warnings below seriously.

What forms does Osuyu come in?

The plain dried fruit is the base form. It is boiled in water to make a bitter decoction (a strong tea).

You may also meet it as:

Granules or powder made from a boiled extract. Small pills. A part of ready-made formulas such as Osuyu-tang (known as Goshuyu-to in Japan).

Much of the fruit sold is processed first, often soaked in licorice water. This is done to make it less harsh on the stomach. It is rarely sold as a stand-alone supplement in the West.

Where it comes from:

Osuyu has a long and wide record in East Asia. It appears in the Shang Han Lun, a Chinese text from about 200 CE, as Wu Zhu Yu.

Korean doctors took it up early. It is listed in the Donguibogam of 1613, Korea's best-known medical book.

Later Sasang medicine gave it mainly to the Soeumin type. That is a body type seen as having a cold, weak stomach. Japanese Kampo medicine uses it too.

What does Osuyu help with?

• Stomach and belly pain that feels cold: This is the classic use. Korean texts give it for dull belly pain that eases with a hot pack or a warm drink. We found no human trial testing the fruit on its own for this.
• Nausea and vomiting: Old texts use it for watery vomiting and for bringing up clear fluid. Animal work hints at an anti-sickness effect. No published human trial backs this use for Osuyu alone.
• Headache with cold hands and feet: The formula Osuyu-tang is a well-known headache remedy in Korea and Japan. Small studies of that whole formula exist, but they cannot show what this one fruit does. Do not use it in place of care for a new, severe or sudden headache.
• Early-morning diarrhoea: Tradition pairs it with other warming herbs for loose stools just before dawn. This is a pattern-based use, not a tested one. No human trial supports it.
• Period pain with a cold, cramping feel: It appears in several classical formulas for cramping period pain. Evidence here is limited to tradition and to lab work on smooth muscle. Get checked if your period pain is new, worsening or very severe.
• Cold hands and feet: Warming herbs like this one are given for a body that feels cold all over. Animal data on blood vessels is suggestive only. Cold, pale or numb fingers that come in attacks need a doctor's opinion.

Which foods are rich in Osuyu?

Osuyu is a medicine, not a food. You will not get it from a normal diet.

What are the side effects of Osuyu?

• Burning or heat in the stomach
• Heartburn
• Dry mouth and thirst
• Nausea or more stomach upset
• Dizziness or a light head
• Headache
• Blurred vision
• Skin rash or itching
• Signs of liver trouble: yellow skin or eyes, dark urine, pain under the right ribs

Good to know:

Most reports are mild and settle when you stop. Stomach burning and dry mouth are the common ones.

Classical Korean and Chinese texts list this fruit as slightly toxic. That warning is old, but it is not empty. Animal studies at high doses show liver damage, and the fruit is one reason some East Asian herb formulas are watched for liver effects.

Liver harm has not been well counted in people taking normal doses inside a formula. Treat it as a real but unmeasured risk. Stop at once if your skin or eyes turn yellow.

How much Osuyu should you take?

• Recommended daily: Korean practice uses about 1.5 g to 4.5 g of the dried fruit a day. It is boiled in water and split across two or three doses. No trial has set a safe or useful dose. Osuyu is almost always used inside a formula, not alone. Do not take more than a licensed practitioner gives you. Higher amounts raise the risk of harm.
• Best time of day: Take it warm, split between morning and evening. For diarrhoea that wakes you near dawn, tradition gives the dose in the evening.
• With or without food: Take it with food or just after eating. It is harsh and burning on an empty stomach.
• Time to effect: Some people report a change in sickness or cold belly pain within hours to a few days. There is no trial data on this. If nothing has shifted in one to two weeks, stop.
• How long to take it: Short courses only. Tradition uses it for days to a few weeks, then stops. Reassess after two weeks. If your symptoms have not changed, stop and get advice. Long-term daily use has not been studied, and the liver questions below make it a poor idea.