🌸Korean Traditional Medicine

Japanese Knotweed (Hojangsaeng)

Reynoutria japonica

About Japanese Knotweed (Hojangsaeng)

Japanese Knotweed (Hojangsaeng) (Reynoutria japonica) is a herb used in the Korean Traditional Medicine tradition to help with Inflammation, Liver Support, and High Blood Pressure. The aerial parts and leaves are the parts traditionally used, taken internally.

Botanical background

Reynoutria japonica, synonyms Fallopia japonica and Polygonum cuspidatum, is a large species of herbaceous perennial plant of the knotweed and buckwheat family Polygonaceae. It is commonly known as Asian knotweed or Japanese knotweed. It is native to East Asia in Japan, China and Korea. In North America and Europe, the species has successfully established itself in numerous habitats and is classified as an invasive species in several countries.

Source: Wikipedia, via iNaturalist

Parts used

Aerial Parts · internalLeaves · internal
🍵

Tea / Infusion

1–3 cups daily
  • Steep 1–2 tsp of dried Japanese Knotweed (Hojangsaeng) in freshly boiled water for 5–10 minutes.
  • Cover while steeping.
  • Strain and drink.
💧

Tincture

20–40 drops in water, 2–3× daily
  • Pack dried Japanese Knotweed (Hojangsaeng) into a jar and cover with 40–60% alcohol.
  • Seal and steep for 4–6 weeks, shaking daily.
  • Strain and store in a dark dropper bottle.
💊

Powder / Capsule

500 mg – 1 g, 1–3× daily
  • Grind dried Japanese Knotweed (Hojangsaeng) into a fine powder.
  • Fill size 00 capsules or stir into smoothies or honey.

Pregnancy, Breastfeeding & Children

No herb-specific pregnancy/child safety research is documented for Japanese Knotweed (Hojangsaeng) in our references — the guidance below is based on its general effect category, not research on Japanese Knotweed (Hojangsaeng) itself. Always confirm with a midwife, doctor, or pediatrician.

Pregnancy

Use Caution

This herb is processed through the liver, which is already working harder during pregnancy — generally used cautiously and not at high/concentrated doses without guidance. This is a general, mechanism-based caution, not herb-specific research.

Breastfeeding

Use Caution

Liver-processed compounds can appear in breast milk — generally used cautiously and in moderation.

Children

Use Caution

A child's liver is still developing its full drug/herb-processing capacity — these herbs are generally used cautiously and at reduced, age-appropriate doses.

Contraindications

  • Pre-surgery — discontinue at least 2 weeks prior (potential antiplatelet effect)
  • Active liver disease — monitor liver enzymes with long-term use

Warnings

⛔ Heart & Blood Pressure Medications

May interact with antihypertensive drugs, blood thinners, or cardiac medications. Do not combine without medical guidance.

⚠️ Liver Health

Some herbs used for liver conditions can be hepatotoxic at high doses. Have liver function monitored if using long-term.

⚠️ Allergic Reactions

Discontinue immediately if you experience rash, itching, swelling, or difficulty breathing.

⚠️ Not Medical Advice

This information is for educational purposes only. Always consult a qualified healthcare provider before using herbal remedies.

Drug & herb interactions

Processed by the liver

Watch for: Any medication that is also processed by liver enzymes (ask your pharmacist — this includes many common prescriptions)

Can alter how quickly the body clears certain medications, raising or lowering their effective dose.

May affect blood pressure

Watch for: Antihypertensive medications (ACE inhibitors, beta-blockers, calcium channel blockers, diuretics)

Combined use can push blood pressure too high or too low — monitor readings if you take blood pressure medication.

Where to find in nature

Native region

Korea, China, Japan

Climate

Temperate

Habitat

Mountain forests, hillside farmland, and traditional herb gardens of the Korean peninsula

🌿 To see Japanese Knotweed (Hojangsaeng) growing, visit botanical gardens, university plant collections, or specialist herb nurseries near you. If foraging in the wild, always work with an expert identifier — never consume a plant you are not 100% certain of.

Where to buy

In store

  • Health food stores (Whole Foods, Natural Grocers, Holland & Barrett, GNC)
  • Naturopathic clinics and integrative medicine practices
  • Specialist herbal apothecaries and herbalist practices
  • Farmers markets with herb vendors

Online

iHerb

Wide selection of standardised extracts, capsules, and powders with lab testing

Mountain Rose Herbs

Premium bulk dried herbs — certified organic, ethically sourced

Starwest Botanicals

Large selection of certified organic bulk herbs and powders

Herb Pharm

High-quality liquid extracts and tinctures, rigorous quality standards

Amazon

Convenient — verify brand certifications and check third-party testing

Etsy

Small-batch artisan herbalists, hand-harvested and wildcrafted herbs

Quality tips

When buying Japanese Knotweed (Hojangsaeng), look for: certified organic labelling, clearly stated country of origin, third-party lab testing for heavy metals and pesticides, and a batch expiry date. Standardised extracts offer consistent dosing; bulk dried herbs are more economical for regular use. Avoid very cheap, unlabelled products — quality varies enormously.