How to Read “One person’s medicine is another person’s poison”
Kō no kusuri wa otsu no doku
Meaning of “One person’s medicine is another person’s poison”
“One person’s medicine is another person’s poison” means that something beneficial to one person can be harmful to another.
The same thing can produce completely opposite results depending on the situation or nature of the person receiving it.
This proverb assumes that each person has a different constitution, personality, position, and situation.
It shows the reality that nothing is universally good for everyone, whether it’s health practices, food, advice, or lifestyle habits.
What one person enthusiastically recommends as “wonderful” may not suit someone else at all.
Today, we’re flooded with health information and lifestyle suggestions.
This proverb teaches us the importance of making calm judgments: “Just because it’s good for others doesn’t mean it’s good for me.”
It also warns us not to force what works for us onto other people.
Origin and Etymology
No clear written record of this proverb’s origin seems to exist. However, we can make interesting observations from how the words are structured.
The terms “kō” and “otsu” are traditional Japanese words that indicate order.
In contracts and legal documents, parties are called “kō” and “otsu.” These terms have also been used to show rankings of things.
This impersonal way of naming was likely chosen to express the universal contrast between “one person” and “another person.”
The pairing of “medicine” and “poison” as contrasting words is also striking.
Medicine is meant to heal and promote health. Yet this proverb vividly expresses the paradoxical truth that the same substance can harm another person.
In traditional Chinese medicine, practitioners have long known that the same herbal medicine can have different effects depending on body type.
During the Edo period, many medical books and practical wisdom texts were published.
Some of these mentioned differences in constitution and individual variation.
This proverb likely crystallized from practical medical knowledge and life experience into words.
Within its simple expression lies deep insight that respects individual differences.
Interesting Facts
In the medical world, the truth shown by this proverb has been scientifically proven.
The same medicine can have vastly different effects due to genetic differences.
A drug that works dramatically for one person may not work at all for another, or may cause strong side effects.
This is called “pharmacogenetics” and has become an important field of modern medical research.
The same applies to food. Milk is nutritious for many people.
But for those who cannot break down lactose, it causes digestive problems.
What people understood through experience long ago is now being confirmed by modern science.
Usage Examples
- Strict guidance worked well for him, but one person’s medicine is another person’s poison—the same approach didn’t suit my junior colleague
- Even though early rising is said to be healthy, one person’s medicine is another person’s poison, so it’s important to find a lifestyle rhythm that matches your own constitution
Universal Wisdom
The proverb “One person’s medicine is another person’s poison” contains a fundamental truth about human society.
That truth is the obvious yet often forgotten fact that each person is different.
Humans tend to think that what’s good for them must be good for others too.
We want to recommend methods that brought us success. We want to share things that worked for us with those around us.
These actions come from good intentions. But this proverb teaches that such good intentions can sometimes hurt others.
This proverb has been passed down through generations because humans tend to seek uniform correct answers.
How easy it would be if there were a universal answer: “Just do this and you’ll be fine.”
But in reality, each person has a different answer.
Our ancestors didn’t turn away from this inconvenient truth. Instead, they faced it head-on.
They expressed the difficulty and importance of accepting diversity through the extreme contrast of medicine and poison.
This proverb continues to tell us across time about the importance of respecting differences with others.
It teaches the humility of not imposing our own values on others.
When AI Hears This
Water and oxygen are absolutely necessary for our survival. Yet drinking six liters of water in a short time causes fatal water intoxication.
Breathing pure oxygen for extended periods damages the lungs. So “the same substance for both kō and otsu” becomes medicine or poison depending on dose.
This is the essence of the dose-response curve.
What’s more interesting is that many substances follow an inverted U-shaped curve.
For example, small amounts of alcohol protect the cardiovascular system, but larger amounts destroy the liver.
Exercise is the same—moderate amounts improve health, but excessive amounts lower immunity and increase susceptibility to infections.
Even radiation activates cellular repair mechanisms in tiny doses, but destroys genes in high doses.
This phenomenon of “small amounts stimulate, large amounts destroy” is called the hormesis effect.
The real insight of this proverb is that while it draws attention to “different individuals” called kō and otsu, it actually implies the concept of “different doses of the same substance.”
For a 50-kilogram child and a 100-kilogram adult, the same medicine is appropriate for one but excessive for the other.
For people genetically rich or poor in alcohol-metabolizing enzymes, the same glass becomes medicine or poison.
Biological thresholds are determined by the multiplication of individual differences and dosage.
Ancient people expressed these two variables through the simple contrast of “kō and otsu.”
Lessons for Today
What this proverb teaches modern people is the “wisdom of choice” needed precisely because we live in an information-saturated age.
The internet overflows with countless health methods, success principles, and lifestyle advice.
Someone’s success story is often presented as if it were a universal truth applicable to everyone.
But the phrase “One person’s medicine is another person’s poison” teaches the importance of having your own judgment criteria amid this flood of information.
You need the ability to calmly assess whether something fits your constitution, personality, and situation, without being swept away by others’ evaluations or trends.
At the same time, you need the consideration not to force what worked for you onto others.
What you recommend with good intentions might burden the other person.
This proverb becomes the foundation for tolerance that accepts diversity.
The flexibility to honestly acknowledge “It works for that person, but not for me.”
And the thoughtfulness to humbly say “It’s good for me, but it might be different for you.”
Hints for building such mature relationships are contained within these few words.
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