Herbal Medicine Has Side Effects Too — The Story of Licorice

"Herbal medicine comes from nature, so it has no side effects, right?"

I have never answered "yes" to this question. Answering that way does not help the patient.

Today I want to talk about licorice, known as the gentlest of herbal materials. It is the licorice that goes into more than half of herbal prescriptions and is also used in candy and drinks. And in this article, I am going to tell you how licorice can put a person in danger.

It may sound strange. Why go out of my way to speak of the danger of a medicine I use myself?

Because only someone who knows the danger can use it safely.

What Licorice Really Does

Licorice is known as a "medicine that gently harmonizes." I don't think licorice is used so often because it is gentle.

The old texts wrote licorice down under two headings — harmonizing the other medicines, and slowing what is urgent. Neither is a vague compliment. Looked at today, they point to two different jobs.

Harmonizing — it regulates the other medicines. While the herbs are decocted together, licorice affects how the other ingredients come out into the liquid. And once inside the body, it settles the lining of the gut, evening out how the other herbs are absorbed and metabolized. That is why licorice sits in so many prescriptions. Not because it is gentle, but because it levels the ground so the other medicines can do their work.

Slowing what is urgent — it takes the edge off. Looked at today, that place is the ion channel. Licorice's compounds have been reported to press on the door calcium comes through, and to pull potassium back toward balance. A muscle seizing up and a nerve firing too readily are both things those ions do. The old word for it — slowing what is urgent — sits right on top of this.

What the old practitioners pressed into two words turns out, today, to be two different mechanisms.

When somewhere in the body is frozen in a startled state—when nerves fire more than necessary, when a mucous membrane reacts excessively, when a muscle suddenly clenches—licorice softens that urgent reaction.

What is interesting is that its action can be quite fast. Licorice's main component has to be metabolized in the body to become active. By the theory, it should take time. Yet in practice there are cases where relief comes quickly.

That is not only my impression. There is an old formula in which licorice makes up half the name. It is used when a leg suddenly cramps and will not straighten, and the old record puts the result like this — "the leg straightens at once." Someone wrote the speed down eighteen hundred years ago.

I understand the reason this way: licorice does its work at the spot it touches, before it spreads through the whole body via the blood. Right at the spot it contacts the mucous membrane, it prevents the over-sensitized cells from pouring out substances. Because it does not need to travel through the whole body, it is fast.

But That Very Licorice

Now to the main point.

Licorice contains a component called glycyrrhizin. It is the component that gives the sweet taste. This component interferes with the work of one enzyme in the body.

That enzyme's original job is to turn off a hormone called cortisol on time. Cortisol is a hormone that should be used when needed and then switched off soon after. But when licorice interferes with that switch, cortisol stays on longer than scheduled.

Cortisol left on too long does the wrong thing in the kidneys. It holds on to sodium and water, and it sends out potassium.

So this is what happens:

What happens in the body	What shows on the outside
Sodium and water accumulate	Swelling, blood pressure rises
Potassium is lost	No energy, muscles go weak
If more potassium is lost	Heartbeat becomes irregular

The last row matters. Potassium is essential for the heart to beat regularly. If it runs seriously low, arrhythmia can occur.

The medicine said to be the gentlest can, used long and in large amounts, affect the heart. This is not a hypothesis but a well-established fact.

The Real Reason I Tell This Story

Here is one situation I dread.

In an earlier article I spoke of long-standing diarrhea. When diarrhea persists, potassium is lost along with water. The person is already in a potassium-deficient state.

What happens if you give such a person a medicine containing licorice for a long time? More potassium is lost. What is already low goes even lower.

Licorice has long been read as the herb that harmonises and softens. That is where the impression of mildness comes from. But when modern pharmacology put a name to that place, the direction turned out to be unexpected. Licorice is not on the side of protecting potassium. It is on the side of sending it out.

Herbs whose mild impression runs this far from what they actually do are not common.

So Here Is What I Do in the Consultation Room

These are the things I check before making up herbal medicine for you.

I ask whether you take blood-pressure medication. Those taking diuretics that increase urine, in particular, may already be low in potassium.

I ask whether you take heart or arrhythmia medication. When potassium drops, the risk of these drugs increases.

I ask whether you have had long-standing diarrhea or vomiting. I need to confirm whether you are already in a depleted state.

I decide how long you will take the medicine. Using it briefly and using it for several months are different stories.

And I tell you to let me know right away if the following symptoms arise:

• Your face or legs swell
• Your blood pressure rises above usual
• You feel unusually drained and your muscles have no strength
• Your chest pounds or your pulse is uneven

These are not "part of the process of getting better." This is not something to endure by calling it a healing crisis. You should stop the medicine and contact me.

So Should Licorice Not Be Used?

No. I use licorice. Often.

The danger comes not from the component itself but from the amount, the duration, and that person's condition. Used briefly, in an appropriate amount, for the right person, licorice is a good medicine.

A place the old practitioners had already noticed

There is one more thing I want to say.

The old texts list pairs not to be used together. Four of them are named as licorice's opposites — and all four happen to be medicines that drive water out of the body. And one old formula built from those medicines leaves licorice out — the one herb that sits in about three quarters of all prescriptions — and puts jujube in its place. The jujube became the formula's name.

That same ion regulation comes back here. Holding on to sodium means holding on to water. It runs straight against a medicine meant to drive water out.

The old practitioners cannot have known this mechanism. And yet they picked out exactly the four that collide, and left it out at exactly the place it had to be left out. They did not use it knowing. They used it having watched. When I come across something like this, I find myself looking at it for a long while.

And this explains licorice's two faces. Slowing what is urgent and holding water until you swell happen in two different rooms of the body. But both are written in the language of ions. That is what it means to say no herb is only good, and none is only bad.

This connects to what I said in another article. What burdens the liver is not the category we call "herbal medicine," but a specific substance entering at a specific concentration for a specific length of time. The same is true of licorice.

And one more thing. Licorice turns up in sweets and drinks as well. Count only the medicine from the clinic and the arithmetic comes out wrong. That is why it helps to tell me what you are taking.

To Speak Honestly

The mechanism of licorice's side effects that I described in this article is a well-established fact. It is not a hypothesis I devised.

By contrast, my explanation of why licorice works so quickly—that it does its work at the spot it touches before circulating through the blood—still has the character of a hypothesis. There is supporting evidence from the laboratory, but it has not been sufficiently confirmed in humans.

I try not to mix these two together. What is established, as established; my interpretation, as my interpretation.

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The reason herbal medicine is safe is not that its components are weak. It is because it hands the body a signal of a size the body can bear.

Yet even that signal, sent large and for a long time, wears the body out. That it came from nature does not mean it is safe. Knowing who uses what, how much, and for how long—that is what creates safety.

I hope you receive your medicine from someone who knows this. I study in order to be that person.

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Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)