What is Koi?

Koi is malt sugar. It is a thick, sweet syrup made from grain, most often sticky rice broken down by barley malt. In Kampo, the herbal medicine of Japan, Koi counts as a drug in its own right, not just a sweetener.

Koi is used for pain and cramps in the belly. It suits the kind of pain that eases when you press or warm the spot. It is also used to build up people who are thin, pale, tired or slow to heal.

You will meet it most often inside a Kenchuto formula, such as Shokenchuto. Other names for it are Saccharum granorum, malt sugar, maltose syrup, mizuame and Yi Tang. In Kampo terms it is sweet and warm, and it is said to tonify, or build up, a weak middle.

Here is the honest verdict. Koi has a long, steady record in Kampo, but almost no human trial data of its own. Long use in a tradition is not proof that a thing works.

How does Koi work?

No one has shown how Koi works in the body. That is the plain truth.

Kampo texts explain it in their own terms. Koi is sweet and warm. Sweet, warm drugs are said to relax a tight, cramping belly and feed a weak middle burner, which is the old name for the digestive core.

A modern guess is simpler. Koi is mostly maltose, a sugar. It gives quick fuel, adds body to a drink, and makes a bitter formula easier to swallow.

Sugar also slows how fast the stomach empties. That could soften a cramp. None of this has been tested in people taking Koi on its own.

So treat the mechanism as a story, not a fact. What we can say is that Koi is food-like, mild, and easy on most stomachs.

What forms does Koi come in?

Koi comes in three main forms.

The first is the classic thick amber syrup, sold in Japan as mizuame. The second is a dried maltose powder, which is what most packaged Kampo granules use. The third is Koi already blended into a finished formula, such as Shokenchuto or Daikenchuto granules.

One sourcing note. Syrups made from brown rice can carry small amounts of inorganic arsenic, a metal that is harmful over the long term. Buy from a maker that tests its raw material, and do not use large daily amounts for months on end.

Where it comes from:

Koi comes from Chinese medicine and was adopted whole by Japan. It appears in the Shanghan Lun and the Jingui Yaolue, works from around 200 CE, as the key drug in Xiao Jian Zhong Tang.

Japanese Kampo doctors kept that formula and called it Shokenchuto. Koi stayed in the same role for centuries: sweet, warming, and aimed at a weak, cramping belly.

It is still listed in the Japanese Pharmacopoeia today and is a normal part of licensed Kampo prescribing.

What does Koi help with?

• Cramping belly pain that eases with warmth or pressure: This is the classic use and the reason Koi exists in Kampo. Shokenchuto, built around Koi, has been given for this pattern for about 1,800 years. The evidence is tradition and clinical habit, not trial data. No published human trial has tested Koi on its own for belly pain.
• Weakness, tiredness and poor weight gain in frail people: Kampo calls Koi a tonifying drug, meaning it is used to build a person back up. It is chosen for people who are thin, pale and easily worn out. Some of the effect is simply calories, since Koi is sugar. There is no trial showing it improves strength or weight beyond what any energy source would do.
• Poor appetite and slow growth in thin children: Shokenchuto with Koi is a long-standing choice for underweight, tired children with a sore belly. Its sweetness also makes the medicine easier for a child to take. This rests on tradition and on doctors' reports, not on controlled trials. A child who is not growing well needs a doctor's assessment first.
• Dry, tickly cough with a weak, tired feeling: Classical texts say sweet, moist drugs soothe a dry throat and chest. Koi is used this way in a few older formulas. This is the thinnest of its uses. There is no human trial support, and a sugary syrup coating the throat may explain any comfort it gives.
• Constipation after surgery (as part of a Kenchuto formula): Daikenchuto, which contains maltose powder, is widely used in Japanese hospitals to help the bowel restart after abdominal surgery. Human trials exist for that whole formula. Credit for any effect is usually given to the other drugs in it, such as ginger and Japanese pepper. Koi's own share, if any, is unknown.

Which foods are rich in Koi?

1. Barley malt syrup: the closest everyday food to Koi
2. Mizuame (Japanese rice syrup): the same product, sold as a sweetener
3. Malt extract spreads and malted drink powders: high in maltose
4. Malted barley in beer wort: maltose is the main sugar there
5. Bread crust and toasted grain: small amounts of maltose form during baking

Practical Tips:

Eating these foods is not the same as taking a Kampo formula, and none of them carry the other drugs a formula relies on.

What are the side effects of Koi?

• Bloating and wind
• Loose stools or mild diarrhoea, mostly at higher amounts
• Feeling full or slightly sick if your belly is already swollen
• A rise in blood sugar, which matters if you have diabetes
• Tooth decay with long daily use, as with any sugar
• Weight gain if large amounts are taken for a long time
• Rare allergic reaction in people sensitive to barley or wheat

Good to know:

Koi is one of the gentlest items in the Kampo cabinet, and most people notice nothing at all.

The two effects worth planning for are gut gas and blood sugar. Both are dose-related, and both settle when you stop.

Serious harm from Koi itself has not been reported. Any severe reaction is far more likely to come from another drug in the formula.

How much Koi should you take?

• Recommended daily: There is no dose set for Koi as a standalone supplement. It is dosed as part of a formula. In traditional Kampo practice, Shokenchuto carries about 20 g of Koi per day, split across two or three doses. Packaged Daikenchuto granules carry roughly 10 g of maltose powder per day. So a normal daily range inside a formula is about 10 g to 20 g. Do not treat that as a licence to spoon syrup from the jar; at that point it is simply sugar.
• Best time of day: Kampo formulas are usually taken two or three times a day, spaced through the day. Many practitioners give the evening dose before bed when night-time belly cramps are the problem.
• With or without food: Kampo formulas are traditionally taken before meals or between meals, on a fairly empty stomach, with warm water. If it makes you feel sick or bloated that way, take it with food instead.
• Time to effect: For cramping belly pain, people often report easing within a few days to two weeks. For tiredness and weight, judge over three to four weeks. If nothing has changed by four weeks, it is unlikely to.
• How long to take it: Kampo formulas holding Koi are often taken for two to four weeks, then reviewed. If belly pain, appetite or energy have not shifted at all by four weeks, stop and rethink with your practitioner. Long runs of months at a time are used in Japan, but only under a doctor who is checking how you are doing. If you have diabetes, review sooner and check your blood sugar readings.