What Is Japanese Knotweed, and Should You Try It?

What is Japanese knotweed?

Japanese knotweed, also known as Fallopia japonica, Reynoutria japonica (R. japonica), and Polygonum cuspidatum (P.cuspidatum), is a perennial plant native to China, Taiwan, Japan, and North and South Korea (1).

This plant was first introduced to Europe in the mid-19th century by a Bavarian exotic plant dealer. Japanese knotweed was likely brought to the United States in the 1800s. You can find it in 42 U.S. states as well as in 8 provinces in Canada (2, 3, 4).

Japanese knotweed reaches up to 15 feet (4.5 meters) tall and grows in dense rows. Because of its bamboo-like stems, it’s sometimes called Japanese bamboo (4).

Adapting to a number of habitats and spreading quickly, the plant requires very little to survive, pushing out native plant species. The roots of the plant can spread up to 65 feet (20 meters) or more.

This is why Japanese knotweed is on the list of the 100 most invasive alien plant species (5).

Even though this plant is highly invasive and poses a threat to native plant species, it does contain a variety of beneficial plant compounds and is an important medicinal plant in traditional medicine systems in China, Japan, and Korea (5).

For example, the dried root of Japanese knotweed has been used for medicinal purposes in China for thousands of years.

The dried root of Japanese knotweed is known as Hu Zhang in the Pharmacopoeia of the People’s Republic of China, an official compendium of drugs, which includes both Traditional Chinese medicine (TCM) and Western medicine (6, 7).

TCM practitioners prescribe Hu Zhang — usually in combination with other TCM herbs — to treat a variety of medical conditions including coughs, jaundice, inflammatory disorders, congestion, high blood lipid levels, and even snake bites (7, 8).

Summary

Japanese knotweed is a highly invasive plant that’s been used as a natural treatment in traditional medicine systems like TCM for thousands of years.

Compounds found in Japanese knotweed

TCM practitioners prescribe the roots of Japanese knotweed because they provide concentrated sources of therapeutic plant compounds.

For example, Japanese knotweed proves rich in resveratrol, piceatannol, polydatin, and other anthranoids like emodin (9).

It also contains flavonoids including quercetin, rutin, apigenin, isoquercitrin, reynoutrin, hyperoside, and kaempferol (1, 7).

However, the most studied compounds of Japanese knotweed rhizomes are emodin and resveratrol.

Research shows that these compounds have anti-inflammatory, antimicrobial, antioxidant, and neuroprotective qualities (1).

Plus, studies may suggest that extracts from various parts of the Japanese knotweed plant including the roots, rhizomes, and stems may offer therapeutic benefits.

Summary

Japanese knotweed is a concentrated source of therapeutic plant compounds like polydatin, emodin, physcion, and resveratrol, which may offer anti-inflammatory and antioxidant benefits.

Does Japanese knotweed have health benefits?

Although Japanese knotweed is regularly used to treat ailments in traditional medicine systems like TCM, human evidence supporting its medicinal value remains inconclusive.

While some test tube and rodent studies suggest that Japanese knotweed may offer health benefits, there are only a few human studies that investigate the effects of Japanese knotweed supplements.

An older study in 20 male basketball players found that 6 weeks of supplementation with 200 mg of Japanese knotweed significantly reduced markers of inflammation compared to a control group (10).

Keep in mind that this extract was standardized to contain a high level of resveratrol, which has potent anti-inflammatory effects. The effects of this treatment may very well have been from the resveratrol alone — not the Japanese knotweed (11).

Another study in 20 healthy adults found that treatment with 200 mg of Japanese knotweed reduced inflammation markers in participants’ blood levels compared to a placebo group (12).

Test tube studies have demonstrated that Hu Zhang extract (HZE) has powerful anti-inflammatory effects, namely suppressing inflammatory proteins from forming in your blood (13).

Findings from other test-tube studies suggest that Japanese knotweed extracts and compounds derived from Japanese knotweed may offer antiviral benefits as well (14, 15).

Because of the plant’s high content of anti-inflammatory compounds, some rodent studies have found that Japanese knotweed extracts may protect against blood vessel damage, ulcerative colitis, and other inflammatory conditions (16, 17, 18, 19).

Although these results are promising, more human research is needed.

Summary

Limited research in humans suggests that Japanese knotweed supplements may be effective for suppressing inflammatory markers, but more studies are necessary to determine how this plant affects human health.

Is Japanese knotweed safe?

Unfortunately, there’s currently no research investigating either the safety or toxicity of Japanese knotweed supplements.

However, a study investigating the effects of Hu Zhang granules in people with gouty arthritis — a type of inflammatory condition that impacts the joints — is currently underway in Shanghai and is expected to be completed by 2023.

Hu Zhang granules is a TCM prescription that contains Japanese knotweed as well as 11 other ingredients including Angelica and Notopterygium (20).

The study will investigate the efficacy and safety of the treatment and may help identify side effects related to the ingestion of Japanese knotweed.

It’s important to note that Japanese knotweed has been used in TCM for thousands of years and hasn’t been associated with serious side effects.

The few human studies investigating the effects of oral supplementation with Japanese knotweed did not report adverse side effects (10, 13).

However, this does not mean that Japanese knotweed supplements are safe or appropriate for everyone.

Because insufficient information exists on side effects, medication interactions, and safe dosage, people who are taking medication, those who are pregnant or breastfeeding, children and teens, and those with medical conditions shouldn’t take Japanese knotweed products.

If you’re interested in taking Japanese knotweed, it’s important to consult a trusted healthcare provider first to learn of any potential risks.

Summary

Although the few recent human studies conducted haven’t reported adverse side effects related to Japanese knotweed supplementation, more research on the safety and potential toxicity of Japanese knotweed is needed.

The bottom line

Japanese knotweed has been used as a treatment in traditional medicine systems for thousands of years.

Even though limited evidence from human, rodent, and test-tube studies suggest that Japanese knotweed provides anti-inflammatory benefits and other therapeutic effects, more research is needed to fully understand its safety and effects on your health.

If you’re interested in using Japanese knotweed products, it’s important to get advice from a healthcare provider who’s familiar with herbal supplements.

They can help determine whether Japanese knotweed supplements prove to be safe, effective, and healthy additions to your healthy diet and lifestyle.