Educational information, not medical advice — ask your doctor or midwife.
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.
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.
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.
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.
See a doctor if belly pain is sharp, sudden, or getting worse, if you have a fever, if you cannot pass stool or wind, or if there is blood in your stool or vomit. Go to hospital straight away for any of these.
Also see a doctor if you have diabetes and your blood sugar readings climb while taking it, if you lose weight without trying, or if your belly pain has not improved after four weeks.
Get urgent help for muscle weakness, cramp, a thumping or uneven heartbeat, or swelling in the ankles while taking a Kenchuto formula. These can be signs that the licorice in it has dropped your potassium too low.
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 Koi 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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