What is Kososan?

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.

How does Kososan work?

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.

What forms does Kososan come in?

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.

Where it comes from:

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.

What does Kososan help with?

• Early common cold, in the first day or two: This is the classic use, and the one with the longest record. Kampo texts pick Kososan over stronger cold formulas for people who are frail, chilly, or have a delicate stomach. Human trial evidence for this use is very thin, so treat it as comfort care and not as a way to shorten an illness.
• Low mood and worry with chest tightness: Kampo practice uses Kososan for a stuck, blocked feeling in the chest and throat that comes with low mood. Most of the research here is in mice under stress, not in people. Do not use it in place of care for depression, and do not stop a prescribed antidepressant to try it.
• Poor appetite and queasiness linked to stress: Citrus peel and ginger in the mix have a long record for settling the stomach. Evidence for this specific formula is traditional rather than trial-based.
• Hives after eating fish or shellfish (traditional use): Old texts list perilla for itchy rashes after eating fish or crab. This is a historical note only. A rash after seafood can be the start of a serious allergic reaction, so get medical help rather than treating it with a herb.

Which foods are rich in Kososan?

1. Perilla (shiso) leaf: the same leaf used in the formula, eaten fresh with sushi and pickles
2. Fresh and dried ginger: the same herb, in a much smaller kitchen amount
3. Dried citrus peel: used in cooking and in some teas
4. Licorice sweets and licorice root tea: contain the same glycyrrhizin that drives the safety warnings

Practical Tips:

Kitchen amounts of shiso, ginger and citrus peel are not a concern, but licorice sweets and licorice tea add to the total and are worth cutting out while you take this.

What are the side effects of Kososan?

• Skin rash, itching or redness
• Nausea, stomach discomfort or loose stools
• Swelling in the ankles, hands or face from held-on water
• A rise in blood pressure
• Low potassium in the blood, which can cause muscle weakness, cramp or an odd heartbeat
• Muscle pain and weakness (rare, and a reason to stop at once)
• Liver irritation, seen on a blood test (rare)

Good to know:

Most people who take Kososan for a few days have no trouble. Mild stomach upset and rash are the common complaints.

The effects worth watching come from the licorice root. Over weeks, licorice can make the body hold salt and water and lose potassium, a pattern doctors call pseudoaldosteronism (a false hormone-like effect that raises blood pressure and drops potassium). Signs are puffy ankles, a higher blood pressure reading, muscle cramp or weakness.

This is more likely with high doses, long use, in older people, and if you take other products containing licorice.

How much Kososan should you take?

• Recommended daily: In Japan, the usual adult amount is about 7.5 g of dried extract granules per day, split into two or three doses. Home-boiled teas are dosed differently. Follow the label on your product or the amount your prescriber gives you. There is no agreed dose outside Japanese practice, and strengths vary between brands. Children's doses are lower and should be set by a doctor.
• Best time of day: Usually split across the day, morning, midday and evening. For a cold, the first dose is traditionally taken as soon as symptoms start.
• With or without food: Kampo granules are traditionally taken before meals or between meals, with warm water. If it upsets your stomach, take it with food instead.
• Time to effect: For cold symptoms, any effect would be felt within a day or two. For mood or appetite, Kampo practice expects weeks rather than days. Neither timeline is backed by good trials.
• How long to take it: For a cold, it is meant as a short course of a few days. Stop once you are better. For low mood or stomach upset, Kampo prescribers often review after two to four weeks. Do not stay on it for months without a check-up, because the licorice in it can build up its effect on blood pressure and potassium over time.