Educational information, not medical advice — ask your doctor or midwife.
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Kososan is a Japanese herbal formula used at the very start of a common cold, and for low mood with a tight, blocked feeling in the chest. It is a Kampo formula on the MHLW list of 148 Kampo medicines that Japan's health system pays for.
It is a mix of five plants. Perilla leaf (shiso) and cyperus root are the two main ones. Licorice root, dried citrus peel and ginger make up the rest.
Kampo doctors tend to pick it for people who tire easily, feel chilly, or have a weak stomach. Here is the short verdict: the formula has a long record of use, but good human trials are almost absent. Long use in a tradition is not proof that a remedy works, and that caveat applies to everything on this page.
No one has shown how Kososan works in the body. What follows is the thinking behind it, not proven fact.
In Kampo terms, the formula is said to move stuck ki (the tradition's word for the body's flow of energy) and to push a chill out through the skin. That is a traditional idea, not a measured process.
In the laboratory, perilla and cyperus contain oils and plant acids that calm nerve cells and lower markers of swelling in animals. Mouse studies suggest the mix may soften the effect of stress hormones. Animal results often fail to repeat in people, so treat this as a hint and nothing more.
One part does have a known body effect. Licorice root contains glycyrrhizin, which makes the kidneys hold on to salt and water and drop potassium. That is why the safety section below matters.
The usual modern form is a dried extract granule. It comes in single-dose paper sachets, often 2.5 g each, made by licensed Japanese makers.
Other forms you may meet:
Fine powder or tablets, for people who dislike granules.
A raw herb pack boiled in water at home to make a tea, the older way of taking it.
Strength differs a lot between makers and between a granule and a home-boiled tea. Check the label rather than assuming one spoonful equals another.
Kososan comes from a Chinese state formulary, the Taiping Huimin Heji Ju Fang, printed around 1107 CE in the Song dynasty. Its Chinese name is Xiang Su San.
Japanese doctors took it up and it became a standard Kampo prescription, especially in the Edo period. It is still prescribed in Japan today and sits on the national insurance list of 148 Kampo formulas.
Stop taking it and see a doctor if your ankles, hands or face swell, if your blood pressure climbs, or if you get muscle cramp, weakness or muscle pain. These can be signs that the licorice is pushing your potassium too low.
Get urgent help if you have chest pain, a racing or irregular heartbeat, trouble breathing, a spreading rash with swollen lips or throat, or dark cola-coloured urine.
See a doctor rather than continuing on your own if cold symptoms last more than a week, if you run a high fever, or if low mood is deep, lasting, or brings thoughts of harming yourself.
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 Kososan 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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