What to Know About Japanese Knotweed

Japanese knotweed (Fallopia japonica) is a perennial herb native to parts of Asia. It has been used in traditional medicine for centuries, although scientific evidence supporting its health benefits is limited.

Parts of the plant (e.g., roots, stems, leaves, and flowers) contain many bioactive compounds thought to benefit human health. These compounds are believed to have antioxidant, anti-inflammatory, antiviral, anticancer, and antibacterial properties.

This article covers what you need to know about Japanese knotweed, including its compounds and research surrounding the herb's potential health benefits.

What Is Japanese Knotweed?

Japanese knotweed is an herbaceous perennial plant native to Asia. It is part of the Polygonaceae family and is sometimes called Reynoutria japonica or Polygonum cuspidatum.

It was first introduced to the United States in the 1800s as an ornamental plant. However, it soon became recognized as an invasive species due to its ability to grow rapidly and almost anywhere.

Despite its invasive nature, Japanese knotweed has been used for centuries for its medicinal properties. However, research on Japanese knotweed is limited, and, therefore, many health claims surrounding it are not supported by strong scientific evidence.

Compounds in Japanese Knotweed

Japanese knotweed is known to contain a long list of bioactive compounds. Many of these compounds have been linked to potential health benefits.

Bioactive compounds are prevalent in the leaves, stalks, and roots of the Japanese knotweed plant. Polyphenols and other antioxidants (compounds that help remove potentially harmful substances) account for much of the bioactive activity of Japanese knotweed. In fact, Japanese knotweed has been found to contain more antioxidant activity than many other plant species.

Of note, Japanese knotweed is especially high in resveratrol, a polyphenol found in red wine and various foods that has been associated with antitumor, anti-inflammatory, and heart-protective effects, among others.

The most notable compounds present in Japanese knotweed include:

• Flavan-3-ols (including catechin)
• Phenolic acids (including caftaric acid and anthraquinones)
• Flavones and flavonols (including quercetin and luteolin)
• Stilbenes (including resveratrol)

Japanese knotweed may have medicinal benefits, largely due to these bioactive compounds.

Does Japanese Knotweed Have Health Benefits?

In traditional Chinese medicine (TCM), Japanese knotweed has been used as an herbal remedy for centuries to treat such ailments as:

• Inflammation
• Various infections
• Jaundice (excess bilirubin in the blood, marked by yellowing of the skin and whites of the eyes)
• Skin burns
• Hyperlipidemia (high lipid levels in the blood)

Compounds found in Japanese knotweed, like stilbenes, anthraquinones, and flavonoids, are thought to provide pharmacological effects. However, research on the potential medicinal benefits of Japanese knotweed is extremely limited.

For the most part, studies have primarily been performed in laboratory settings rather than on humans. And while we can learn from such studies, human research is needed on Japanese knotweed before it can be recommended as an effective alternative medicine.

In TCM, Japanese knotweed is commonly used to treat certain types of viral infections. However, there isn't much scientific evidence to back this up.

Lab studies have used roots and stems from Japanese knotweed to understand better what compounds in Japanese knotweed may provide anti-inflammatory activities. According to the study, resveratrol and glucosides showed the highest levels of anti-inflammatory effects. These compounds were found to inhibit inflammatory substances in the body.

Other lab studies have suggested that Japanese knotweed may have antiviral and anticancer effects as well.

Keep in mind that supplements and herbs should never replace standard medical treatments.

Is Japanese Knotweed Safe?

Japanese knotweed is generally considered safe, but it may cause side effects, and certain precautions may need to be taken.

Because there are so few human trials, not enough is known about the safety of Japanese knotweed. It's reassuring that Japanese knotweed has been used for many years in TCM without reports of serious adverse events. However, some of the compounds in Japanese knotweed have known possible side effects.

Resveratrol is a well-researched compound found in Japanese knotweed. With short-term use, resveratrol does not typically cause side effects. However, long-term use or high doses of resveratrol at 2.5 grams or more per day may cause:

• Nausea
• Vomiting
• Diarrhea
• Liver dysfunction

Japanese knotweed is not considered toxic, but taking large doses may increase your chance of side effects. The best way to avoid potential side effects is to use Japanese knotweed only as directed.

Children, people who are pregnant, people who are breastfeeding, and people with medical conditions may need to avoid using Japanese knotweed. This is because there is not enough reliable information to know if the herb is safe for people in these sensitive populations.

Always talk with a healthcare provider before starting a new herb or supplement, especially if you have a health condition, take prescription medications, are pregnant, or are breastfeeding.

Dosage: How Much Japanese Knotweed Should I Use?

As with other aspects of Japanese knotweed, information regarding safe dosage is not available. This is simply due to a lack of credible research.

In lab studies, the efficacy of Japanese knotweed appears to be dependent on the dose. However, many of these studies have been on specific compounds (like resveratrol and emodin) rather than Japanese knotweed itself.

Until more information is available, be sure to follow dosing directions as listed on the supplement label or as provided by a healthcare provider.

How to Store Japanese Knotweed

For quality purposes, it's important to store Japanese knotweed properly.

Store Japanese knotweed supplements in a cool, dry place and keep them out of direct sunlight. Cupboards and pantries are safe spots to store Japanese knotweed and other herbs or supplements.

You can store fresh Japanese knotweed in the freezer if you don't plan to use it right away.

Dried Japanese knotweed herbs can be stored in a refrigerator or freezer, if desired. Otherwise, store dried Japanese knotweed in a cool, dry place.

Discard Japanese knotweed if it shows any signs of spoilage, such as discoloration or foul smell. Follow any discard directions as listed on the packaging of Japanese knotweed supplements.

Sources of Japanese Knotweed & What to Look For

Fresh or dried Japanese knotweed can be used in cooking and baking. However, it is more commonly used in supplement form.

If you're thinking of using Japanese knotweed, keep in mind that its potential health benefits have not yet been proven through solid scientific evidence. And while Japanese knotweed contains several bioactive compounds that may benefit your health, it is not a required nutrient (like vitamins and minerals). When it comes to your health, nothing beats a well-balanced diet.

Food Sources of Japanese Knotweed

Japanese knotweed is not naturally found in foods, but there are ways to cook and bake with it.

Since Japanese knotweed is so abundant due to its invasive nature, you can forage your own. Fresh Japanese knotweed is not typically sold in stores, but it may be possible to find it at farmer's markets.

Fresh Japanese knotweed can be grilled, cooked in other ways, or eaten raw. Numerous recipes are available online that detail ways to add Japanese knotweed to cooked dishes or baked goods.

Japanese knotweed is said to have a tart flavor, similar to rhubarb.

Japanese Knotweed Supplements

There are some things to keep in mind if you decide to use Japanese knotweed supplements.

Japanese knotweed supplements are sold online and in various health food or supplement stores. You can find Japanese knotweed supplements in the form of powders, capsules, tinctures, and extracts.

Most Japanese knotweed supplements are vegan and gluten-free. However, some capsules may contain gelatin, a substance derived from animals like cows and pigs.

Dietary supplements are not regulated like drugs in the United States. They can cause interactions with medications or have other safety concerns. For this reason, it’s important to be aware of what to look for when choosing a supplement, such as third-party testing, potential drug interactions, and more.

Summary

Japanese knotweed is a perennial herb and invasive species that may have medicinal benefits. It has been used in TCM for centuries, but most of its potential benefits have yet to be proven by strong scientific evidence.

Japanese knotweed is mostly considered safe but some people may need to avoid using the herb and it may cause certain side effects if used improperly.

Talk with a healthcare provider before using Japanese knotweed to learn if it is right for you.