Guan Zhong

What is Guan Zhong?

Guan Zhong is the dried rhizome (underground stem) of certain ferns. Chinese medicine uses it on its own, not as part of a blended product. The name covers several plants.

The one sold most often is Dryopteris crassirhizoma. It is a close relative of the European male fern rhizome.

It was used mainly to expel worms from the gut. The charred herb was used to slow bleeding. During outbreaks of fever, people also added it to folk drinks to try to ward off illness.

Here is the honest verdict, up front. This herb has a long, well-recorded history. But there is almost no modern trial evidence in people.

It is also truly poisonous at doses close to the ones once used. Long use in tradition is not proof that a herb works or that it is safe. That is true here more than with most herbs.

How does Guan Zhong work?

The active compounds seem to paralyse tapeworms and other gut worms. The worms lose their grip on the gut wall and are passed out. This was the basis of its use before modern worm drugs existed.

The same compounds are toxic to human nerve and eye tissue. On their own, they pass from the gut into the blood poorly.

Fat, oil or alcohol taken at the same time raise how much gets in. That is how most serious poisonings happened.

The charred form was used to slow bleeding. The usual explanation is its tannins (plant compounds that tighten tissue). This has not been confirmed in people.

What forms does Guan Zhong come in?

Guan Zhong is sold in a few forms.

- Dried sliced rhizome, simmered into a decoction (a water extract). - Guan Zhong Tan, the charred form, used in tradition for bleeding. - Powdered rhizome, sometimes in capsules or pills.

Two more forms are worth knowing.

- Part of a multi-herb prescription written by a practitioner. - An ether extract of male fern, used in Western pharmacy until the mid-20th century. - That extract has now been withdrawn in most countries.

Where it comes from:

Guan Zhong appears in the Shennong Bencao Jing. That is a Chinese herbal from about the first to second century CE. The herb stayed in use for worms, bleeding and fevers for nearly two thousand years.

The close relative male fern rhizome has its own long record in Europe. Greek and Roman writers described it. Western drug lists carried it into the twentieth century.

It was dropped once safer worm medicines arrived. Reports of blindness and death had built up.

What does Guan Zhong help with?

• Tapeworm and other worms in the gut: This use has the strongest record in history. Male fern rhizome was an official worm medicine in Western pharmacy for decades. Many people believed it worked against tapeworm. It was dropped because the safety gap was small. A dose that expelled the worm was close to a dose that poisoned the person. Modern drugs such as praziquantel and albendazole are far safer and better studied. See a doctor to treat worms.
• Heavy or odd bleeding from the womb (charred form, traditional): Old Chinese texts use the charred rhizome to slow bleeding from the womb, the nose and the bowel. Support comes from classical writing and from practitioner experience. There are no controlled human trials. Heavy or unexplained bleeding from the womb needs a cause found by a doctor. Do not treat it at home with a toxic herb.
• Nosebleed and other minor bleeding (charred form, traditional): The same charred herb was used for nosebleeds and for blood in the stool. The evidence is traditional only. No published human trial shows that it shortens or reduces bleeding.
• Folk use during flu and other outbreaks of fever: Guan Zhong was sometimes added to shared water during outbreaks. People hoped it would stop illness. Some lab studies report action against viruses in cell cultures. Action in a dish does not mean the herb prevents or treats flu in people. No human trial has shown that it does. Vaccines and standard care are the tested options.

What are the side effects of Guan Zhong?

• Nausea, vomiting, belly pain and diarrhoea
• Headache and dizziness
• Blurred vision, colour changes in vision, or loss of sight: sometimes permanent
• Tremor, muscle twitching or seizures (fits)
• Slow or irregular heartbeat
• Liver injury, sometimes with jaundice (yellow skin or eyes)
• Kidney injury with reduced urine output
• Confusion, coma and breathing failure in severe poisoning
• Miscarriage or harm to a pregnancy

Good to know:

These are not rare theoretical risks. Poisoning from male fern rhizome is well documented in the older medical literature, including permanent blindness from damage to the optic nerve (the nerve that carries sight from the eye) and a number of deaths.

Mild stomach upset is the most common reaction. The dangerous effects usually follow a high dose, a repeated dose, or a dose taken with fat, oil or alcohol.

This is one of the more toxic herbs in common traditional use, and it should be treated with the same care as a prescription drug.

Options to discuss with a clinician

If worms are the worry, a doctor can test for them first. Modern worm medicines are well studied, and their doses are known. You can ask your clinician whether one of those suits you.

For heavy or unusual bleeding, a doctor can look for the cause before anything is taken. Some people also ask about gentler traditional herbs, such as yarrow, shepherd's purse or nettle. Raise any of these with your clinician, who can weigh them against your own health and your other medicines.

Graded pages for the options named above:

• Shepherd's Purse — evidence grade insufficient, traditional tier T3