Herbal Monograph
Black walnut
Juglans nigra L.
Juglandaceae (Walnut family)
Powerful antimicrobial hull rich in juglone — traditional vermifuge and antifungal with strong astringent action for weeping skin and intestinal dysbiosis.
Overview
Plant Description
Large, long-lived deciduous tree reaching 20-40 m in height with a trunk diameter of 60-150 cm at maturity. Crown is open, rounded, and spreading in open-grown trees; tall and narrow in forest settings. Bark is dark brown to nearly black, deeply furrowed into rough, diamond-shaped ridges — the source of the common name. Leaves are alternate, pinnately compound, 30-60 cm long, with 15-23 lanceolate, serrate leaflets, each 6-12 cm long; terminal leaflet often smaller or absent; leaves are aromatic when crushed. Monoecious: male flowers in pendulous catkins 8-12 cm long appearing with the new leaves in spring; female flowers small, in terminal clusters of 2-5. Fruit is a large spherical drupe, 4-6 cm diameter, with a thick, fleshy green husk (hull) that turns yellow-green to brown-black as it ripens; the hull contains high concentrations of juglone and tannins that stain deeply on contact with skin. The nut within has an extremely hard, corrugated, thick shell enclosing an edible, richly flavored kernel. Taproot is deep and extensive; lateral roots exude juglone, creating an allelopathic zone (the 'walnut toxicity' zone) that inhibits growth of many plant species within the root zone.
Habitat
Rich, moist, well-drained bottomland soils along rivers, streams, and in mixed hardwood forests. Prefers deep, fertile loams and alluvial soils with good drainage. Tolerates a range of pH (6.0-8.0) but performs best in slightly acidic to neutral soils. Intolerant of shade; requires full sun for optimal growth. Found from lowlands to approximately 1,200 m elevation.
Distribution
Native to eastern and central North America, from southern Ontario and Quebec south to northern Florida, west to Minnesota, Nebraska, Kansas, and central Texas. Most abundant in the Ohio and Mississippi River valleys and the central hardwood forests. Widely planted outside its native range as a timber and nut tree in parts of western North America, Europe, and other temperate regions. Commercially valued for its timber (one of the most prized North American hardwoods) and edible nuts.
Parts Used
Green hull (pericarp)
Preferred: Fresh hull tincture (1:2 in 50-60% ethanol); dried hull powder in capsules
The fresh green hull (outer pericarp of the fruit) is the primary medicinal part in modern herbal practice. It contains the highest concentration of juglone and related naphthoquinones, along with ellagic acid and condensed tannins. The fresh hull is significantly more potent than dried material because juglone polymerizes and degrades with oxidation. Fresh hull tincture is the gold standard preparation. The hull is the basis of the traditional and Eclectic use as a vermifuge and antifungal agent.
Leaf
Preferred: Infusion for topical wash or compress; dried leaf
Leaves contain lower concentrations of juglone and naphthoquinones than hulls, but significant levels of ellagic acid, quercetin, kaempferol, and hydrolyzable tannins. Used primarily as a topical astringent wash or in sitz baths for weeping skin conditions, eczema, and hemorrhoids. The leaf infusion is the basis of the European (J. regia) tradition approved by the German Commission E for mild skin inflammation.
Inner bark
Preferred: Decoction; historically as a fluid extract (now uncommon)
Used historically in Eclectic medicine as a mild laxative and alterative, particularly by Harvey Wickes Felter and John Uri Lloyd. Contains juglone, tannins, and juglandin (a resinous extract). Less commonly used today — the hull is preferred as a more sustainable and potent source. The related species J. cinerea (butternut) was the preferred bark source in Eclectic practice.
Key Constituents
Naphthoquinones
The naphthoquinones, particularly juglone, are the primary bioactive constituents responsible for the antimicrobial, antifungal, and antiparasitic actions of black walnut hull. Juglone's mechanism involves redox cycling in biological systems: it accepts electrons from cellular reductases, generating semiquinone radicals that react with molecular oxygen to produce superoxide and other reactive oxygen species. This oxidative stress is selectively toxic to microorganisms and parasites, which have less robust antioxidant defenses than mammalian cells. The naphthoquinone content is highest in fresh green hulls and declines substantially with drying and oxidation, making preparation timing critical for therapeutic potency.
Tannins
The high tannin content (both hydrolyzable and condensed) is responsible for the strong astringent action of black walnut, particularly in topical applications. Tannins precipitate surface proteins on skin and mucous membranes, forming a protective barrier that reduces inflammation, secretion, and microbial colonization. This astringent mechanism underlies the traditional use for weeping eczema, hemorrhoids, diarrhea, and mouth/throat inflammation. The tannins also contribute to the anthelmintic action — proanthocyanidins can disrupt parasite cuticle proteins and inhibit parasite enzyme function. Ellagic acid specifically has attracted research interest for antimutagenic and chemoprotective properties in preclinical models.
Flavonoids and phenolic compounds
The flavonoid and phenolic compounds provide additional antioxidant, anti-inflammatory, and mild antimicrobial activity that complements the primary naphthoquinone and tannin fractions. These constituents are particularly relevant in the leaf preparations used topically for skin inflammation.
Other constituents
The minor and trace constituents provide supporting roles. The volatile oil fraction contributes aromatic and mild anti-inflammatory properties. The purported iodine content is frequently cited in popular herbalism but analytical data are limited. The nutritive composition of the nut kernel (omega-3 fatty acids, minerals, protein) is relevant as a food but distinct from the hull's medicinal applications.
Herbal Actions
Kills or inhibits the growth of microorganisms
The defining pharmacological action of black walnut hull. Juglone demonstrates broad-spectrum activity against bacteria (including Staphylococcus aureus, Escherichia coli, and Helicobacter pylori in vitro), fungi (Candida albicans, Trichophyton rubrum, Microsporum species), and parasites. The antimicrobial mechanism involves disruption of microbial electron transport chain via redox cycling of naphthoquinones, generating oxidative stress that exceeds microbial antioxidant capacity. The tannin fraction contributes additional antimicrobial activity through protein denaturation and membrane disruption. Fresh green hull preparations are significantly more potent than dried material due to juglone degradation during oxidation.
[3, 4, 5]Tightens and tones tissue, reduces secretions
Strong astringent action due to the high tannin content (15-20% in hull). Tannins precipitate surface proteins on mucous membranes and skin, creating a protective barrier that reduces secretion, inflammation, and microbial access. This action is the basis for topical use in weeping skin conditions, hemorrhoids, mouth and gum inflammation, and as a gargle for sore throat. The astringent effect is also relevant internally for addressing diarrhea and excessive intestinal secretion.
[3, 4]Gradually restores proper body function and increases overall health
Classified as an alterative (blood cleanser) in Eclectic and traditional Western herbal medicine. The alterative action reflects the gradual improvement in tissue health and function attributed to the combination of antimicrobial, anti-inflammatory, and astringent properties working together over time. Traditionally used as part of alterative formulas for chronic skin conditions, lymphatic congestion, and sluggish elimination. The Eclectics considered black walnut bark and hull as a mild alterative that supported liver and bowel function alongside its topical actions.
[3, 4]Prevents or slows oxidative damage to cells
Significant antioxidant activity attributable to the combined polyphenol profile: ellagic acid, gallic acid, quercetin, condensed tannins, and other phenolic compounds. Ellagic acid is particularly noteworthy for its ability to scavenge reactive oxygen species and chelate transition metals that catalyze oxidative damage. The antioxidant action is paradoxical alongside juglone's pro-oxidant mechanism — the therapeutic effect depends on the selectivity of juglone's redox cycling toward microbial cells, while the polyphenol fraction provides antioxidant protection to host tissues.
[4]Promotes bowel movement
Mild laxative effect, particularly from the inner bark and hull, attributed historically to the naphthoquinone and resinous fractions. The related species J. cinerea (butternut) was the preferred Eclectic laxative in the Juglans genus. Black walnut's laxative action is gentle and was valued in traditional practice for supporting intestinal transit during parasite cleansing protocols. Not a primary indication in modern practice.
[3]Promotes wound healing
Topical wound-healing activity supported by the combination of astringent (tannin-mediated tissue tightening), antimicrobial (juglone), and anti-inflammatory (polyphenol) properties. Historically applied as a hull wash or poultice to slow-healing wounds, ulcers, and fungal skin infections. The astringent-antimicrobial combination is particularly well-suited to weeping or infected wounds.
[3, 4]Therapeutic Indications
Digestive System
Intestinal parasites (helminths, pinworms)
The best-known traditional indication. Black walnut hull has been used as a vermifuge (anthelmintic) for centuries in North American folk medicine and by the Eclectics. The mechanism is attributed to juglone's disruption of aerobic respiration in intestinal parasites. Traditionally used for roundworms, pinworms (Enterobius vermicularis), and tapeworms. Typically combined with other antiparasitic herbs (wormwood/Artemisia absinthium, cloves/Syzygium aromaticum) in a synergistic protocol. Clinical evidence is limited to traditional reports and in vitro data; no modern RCTs exist for black walnut as an anthelmintic.
[3, 4, 5]Intestinal dysbiosis and fungal overgrowth
The broad-spectrum antimicrobial activity of juglone extends to intestinal fungi (particularly Candida species) and dysbiotic bacteria. Used in naturopathic practice as part of antimicrobial protocols for intestinal candidiasis, small intestinal bacterial overgrowth (SIBO), and chronic dysbiosis. Typically combined with other antimicrobial botanicals (oregano, berberine-containing plants). Evidence is based on in vitro antimicrobial data and clinical tradition rather than controlled human trials.
[4]Diarrhea and intestinal inflammation
The strong astringent (tannin) action makes black walnut useful for acute and chronic diarrhea with excessive intestinal secretion. Tannins precipitate proteins on the intestinal mucosa, forming a protective layer that reduces fluid loss, inflammation, and microbial adherence. Eclectic physicians used black walnut decoction internally for chronic diarrhea and dysentery. The combined astringent and antimicrobial actions address both the symptom (excess fluid) and potential infectious cause simultaneously.
[3]Skin / Integumentary
Fungal skin infections (tinea, ringworm, athlete's foot)
Topical application of black walnut hull preparations for fungal skin infections is one of the strongest traditional indications. Juglone demonstrates in vitro activity against common dermatophytes including Trichophyton rubrum, T. mentagrophytes, Microsporum canis, and Epidermophyton floccosum. Applied as a hull tincture, wash, or diluted extract to affected skin. The combination of antifungal (juglone) and astringent (tannin) activity is well-suited to moist, weeping fungal infections. Anecdotal clinical support is strong; controlled topical trials are lacking.
[4, 5]Weeping eczema and dermatitis
The strong astringent action of black walnut leaf and hull preparations (wash, compress, sitz bath) is used for weeping, exudative skin conditions. The tannins dry excessive secretions and form a protective protein barrier on inflamed skin. This use parallels the German Commission E-approved indication for J. regia leaf for mild skin inflammation. Best suited for wet, weeping eczema rather than dry, scaly eczema (which would be worsened by astringent drying).
[2, 4]Acne and impetigo
Topical antimicrobial and astringent action applied to bacterial skin infections. Juglone's activity against Staphylococcus aureus (a primary pathogen in impetigo and acne) supports this traditional use. Applied as a dilute wash or incorporated into topical formulations.
[4]Warts and verrucae
Application of fresh hull juice or concentrated hull tincture directly to warts is a well-known folk remedy. The caustic/keratolytic action of juglone may contribute to wart destruction. Anecdotal reports are common; no clinical studies exist. The strong staining is a practical consideration.
[5]Immune System
Candida and fungal infections (systemic support)
Used internally as part of comprehensive antifungal protocols in naturopathic and integrative practice. Juglone demonstrates in vitro fungistatic and fungicidal activity against Candida albicans and other Candida species. Typically used alongside dietary modification, probiotics, and other antifungal botanicals. Internal use for systemic fungal support is based on traditional practice and in vitro data; systemic bioavailability of juglone after oral administration is not well-characterized.
[4]Hepatobiliary System
Sluggish liver and bile insufficiency
Eclectic physicians classified black walnut (particularly the bark) as a mild hepatic stimulant and alterative. The bitter naphthoquinone fraction stimulates digestive and biliary secretions. Used in traditional formulas for sluggish liver function, constipation with pale stools (suggesting bile insufficiency), and as part of alterative protocols for chronic skin disease attributed to impaired hepatic detoxification.
[3]Energetics
Temperature
warm
Moisture
dry
Taste
Tissue States
damp/stagnation, damp/relaxation
In Western vitalist energetics, black walnut is warming and drying — the classic profile for addressing conditions of excess dampness, tissue laxity, and microbial overgrowth. The strong astringent taste reflects the high tannin content and indicates its affinity for tightening boggy, lax, and weeping tissues. The bitter taste signals the naphthoquinone fraction and stimulation of digestive secretions. Black walnut is specifically indicated for damp/relaxation tissue states: weeping eczema, excessive intestinal mucus, fungal overgrowth in warm moist environments, lax hemorrhoidal tissue, and spongy bleeding gums. The warming quality supports circulation to tissue beds that are cold and congested. In Eclectic tissue-state terminology, it addresses the 'relaxed' and 'atonic' conditions of mucous membranes and skin. Constitutionally best suited for individuals with cold, damp, lax tissue tendencies; use with caution in dry, hot, or depleted constitutions where the strong drying and astringent action could be excessively tissue-tightening.
Traditional Uses
Native American medicine
- Cherokee: bark decoction as a cathartic; hull infusion for ringworm and skin infections
- Iroquois: inner bark used for headache, toothache, and as a blood purifier
- Meskwaki: bark used as a laxative and for treating intestinal parasites
- Chippewa: inner bark poultice for wounds and skin sores
- Various tribes used the hull juice as an insect repellent and fish poison (the naphthoquinones are ichthyotoxic)
- Nuts were an important food source; hull dye used for basket-weaving and textile coloring
"Black walnut was widely used across its native range by numerous Native American peoples. Moerman's Native American Ethnobotany database documents uses by at least 14 different tribes, primarily for skin conditions, intestinal complaints, and as a cathartic. The hull juice was used as a fish poison by multiple tribes — a practice based on juglone's toxicity to gill-breathing aquatic organisms. The dual food-medicine relationship with black walnut was central; the nut was a caloric staple while the hull, bark, and leaf served therapeutic purposes."
[6]
Eclectic medicine (American, 19th-20th century)
- Vermifuge: hull preparations for intestinal worms, particularly in children
- Alterative: bark and hull in chronic skin diseases, scrofula, and syphilitic conditions
- Astringent: bark and leaf decoction for diarrhea, leucorrhea, and hemorrhoids
- Topical antifungal: hull wash for ringworm, herpes, and eczema
- Mild cathartic: inner bark for gentle laxation, particularly in combination with alterative formulas
- Gargle: bark decoction for sore throat and mouth ulcers
"Felter and Lloyd (King's American Dispensatory, 1898) described Juglans nigra as 'a mild cathartic, acting somewhat upon the liver' and valued the hull for 'herpetic eruptions, eczema, and various parasitic skin diseases.' The Eclectics distinguished between the bark (mild cathartic and alterative) and the hull (stronger antimicrobial and antifungal). They frequently combined black walnut with other alteratives such as Arctium lappa (burdock) and Rumex crispus (yellow dock) in protocols for chronic skin disease."
[3]
Contemporary Western herbalism
- Antiparasitic protocols: hull tincture as part of the 'black walnut / wormwood / clove' combination popularized for intestinal parasite cleansing
- Antifungal: internal and topical use for Candida overgrowth and dermatophyte infections
- Topical astringent: hull and leaf washes for eczema, hemorrhoids, and fungal skin conditions
- Alterative formulas: included in 'blood-cleansing' and liver-support formulas
- Oral health: hull tincture diluted as a mouthwash for gum disease, canker sores, and oral thrush
"Modern Western herbalists use black walnut primarily as an antimicrobial and antiparasitic agent. The herb gained widespread popular attention through Hulda Clark's parasite cleansing protocols in the 1990s, which, while controversial in their broader claims, brought black walnut hull into mainstream herbal awareness. Practitioners such as David Hoffmann and Matthew Wood continue to value it for its astringent and antifungal properties in more evidence-based frameworks."
Modern Research
Antifungal activity of juglone — in vitro studies
Multiple in vitro studies have evaluated juglone's antifungal activity against clinically relevant fungal pathogens.
Findings: Juglone demonstrates fungistatic and fungicidal activity against Candida albicans, C. tropicalis, Trichophyton rubrum, T. mentagrophytes, Microsporum canis, and Aspergillus niger in disk diffusion and minimum inhibitory concentration (MIC) assays. MIC values for juglone against Candida species range from 3.9 to 31.2 µg/mL depending on the study and strain. The antifungal mechanism involves disruption of mitochondrial electron transport, generation of intracellular reactive oxygen species, and interference with ergosterol biosynthesis in fungal membranes.
Limitations: All data are in vitro. The concentrations achieving antifungal effects in laboratory assays may not be attainable systemically after oral administration. Bioavailability, metabolism, and tissue distribution of juglone in humans are poorly characterized. Topical applications likely achieve effective local concentrations, but systemic antifungal claims are not supported by clinical data.
Antibacterial activity of Juglans nigra extracts
Hull and leaf extracts have been tested against common bacterial pathogens in vitro.
Findings: Black walnut hull extracts demonstrate inhibitory activity against Staphylococcus aureus (including some MRSA strains in limited testing), Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa. Gram-positive organisms generally show greater susceptibility than gram-negative organisms, consistent with the mechanism of action involving cell membrane disruption. The combination of juglone and tannins may provide broader antibacterial spectrum than either fraction alone.
Limitations: In vitro data only. Zone-of-inhibition and MIC methods vary across studies. No standardized extract was used across studies. Clinical antibacterial efficacy in human infections is not established. Should not be considered a replacement for antibiotic therapy in serious infections.
[4]
Ellagic acid — antimutagenic and chemoprotective activity
Ellagic acid, a major polyphenol in black walnut hull, has been studied extensively for anticancer and chemoprotective properties in preclinical models.
Findings: Ellagic acid demonstrates antimutagenic activity in bacterial mutagenesis assays (Ames test) and inhibits chemical carcinogenesis in animal models (skin, lung, esophageal, and colon carcinogenesis). Mechanisms include direct binding and inactivation of certain chemical carcinogens, inhibition of CYP1A1-mediated carcinogen activation, induction of phase II detoxification enzymes (glutathione S-transferase), and antioxidant/free radical scavenging. Ellagic acid also demonstrates antiproliferative and pro-apoptotic effects in cancer cell lines in vitro.
Limitations: Bioavailability of ellagic acid after oral administration is poor due to low water solubility, rapid metabolism, and extensive conversion to urolithins by gut microbiota. The chemoprotective effects observed in animal models at pharmacological doses may not translate directly to clinical practice at dietary intake levels. No clinical trials have demonstrated anticancer efficacy of black walnut hull specifically.
[4]
Anthelmintic (antiparasitic) activity — preclinical evidence
The traditional anthelmintic use has been partially validated by preclinical research on naphthoquinones.
Findings: Juglone and related naphthoquinones demonstrate anthelmintic activity in vitro against various helminth species. The mechanism involves inhibition of parasite mitochondrial enzymes (fumarate reductase, succinate dehydrogenase) essential for anaerobic respiration, which many intestinal helminths rely upon. Naphthoquinones also uncouple oxidative phosphorylation in parasite mitochondria. The tannin fraction may contribute by disrupting the parasite tegument (outer surface).
Limitations: Most anthelmintic studies used isolated juglone or synthetic naphthoquinones rather than whole black walnut hull extracts. In vivo anthelmintic efficacy in human intestinal parasitism has not been evaluated in controlled clinical trials. Effective in vitro concentrations may not be achieved in the intestinal lumen at recommended oral doses. Traditional reports are the primary basis for clinical use.
Preparations & Dosage
Tincture
Strength: Fresh hull: 1:2, 50-60% ethanol. Dried hull: 1:5, 50% ethanol.
FRESH HULL TINCTURE (preferred): Collect green hulls immediately after harvesting, wearing gloves to avoid staining. Chop or slice fresh hulls and fill a jar to approximately 2/3 full. Cover completely with 50-60% ethanol (100-proof vodka works). Ensure all plant material is submerged (oxidation above the liquid line reduces potency). Seal tightly and macerate 4-6 weeks in a cool, dark place, shaking daily. Press and filter through muslin. The resulting tincture should be dark greenish-brown to nearly black. DRIED HULL TINCTURE: Use dried green hull that still retains greenish-brown color. 1:5 ratio in 50% ethanol. Macerate 4-6 weeks.
Fresh hull tincture: 1-2 mL (20-40 drops), 2-3 times daily. For antiparasitic protocols: some practitioners use higher doses (up to 5 mL 2-3 times daily) for short durations (2-4 weeks) under professional supervision.
2-3 times daily, taken with meals to reduce GI irritation.
For antiparasitic use: typically 2-4 weeks as part of a protocol, often with rest periods. For topical or astringent use: as needed. Long-term continuous internal use is not generally recommended.
Not recommended for young children without qualified practitioner guidance. For children over 6 years, some practitioners use 5-15 drops diluted in water, 2-3 times daily for short courses.
Fresh hull tincture is strongly preferred over dried hull preparations due to the instability of juglone. The tincture should be prepared within hours of hull harvest for maximum potency. Once made, the tincture is relatively stable if stored in amber glass away from light and heat. Discard if the tincture has lost its dark color and become pale brown — this indicates juglone degradation. The tincture stains; use a dropper carefully and rinse immediately. Some practitioners add a small amount of vitamin C (ascorbic acid) to the menstruum to help preserve the reduced form of juglone.
Capsule / Powder
Strength: Crude dried hull powder, typically 500 mg per capsule.
Dried green hull powder encapsulated in vegetable or gelatin capsules. Ensure powder is from green-stage hulls that were dried quickly and properly (retain greenish-brown color, not black). Store in airtight, light-protected containers to minimize juglone degradation.
500-1,000 mg of dried hull powder, 2-3 times daily with meals. Some antiparasitic protocols use up to 2,000 mg 3 times daily for short courses (2-3 weeks).
2-3 times daily with meals.
2-4 weeks for antiparasitic protocols. Not generally recommended for continuous long-term internal use.
Not recommended without practitioner guidance.
Capsules are more convenient but likely less potent than fresh hull tincture because juglone degrades during drying. Quality varies significantly between products — look for products specifying green-stage hull, proper drying methods, and analysis for juglone content. Some products combine black walnut hull with wormwood and clove in antiparasitic formulas.
[5]
Decoction
Strength: 2-4 g dried hull or bark per 250 mL water
Add 2-4 g of dried bark or dried hull to 250 mL cold water. Bring to a boil, reduce heat, and simmer 10-15 minutes. Strain. The decoction will be dark brown.
One cup (250 mL), 2-3 times daily.
2-3 times daily.
Short-term use (1-3 weeks) for internal indications.
Not commonly used in children.
The decoction method is appropriate for the hard, woody hull and bark material. Simmering extracts tannins and minerals effectively. For internal use as an astringent for diarrhea, the high tannin content is desirable. For antiparasitic purposes, the tincture is preferred because the ethanol menstruum better extracts juglone.
Infusion (Tea)
Strength: 2-3 g dried leaf per 250 mL (internal); 4-6 g per 250 mL (topical wash)
For leaf preparations: pour 250 mL boiling water over 2-3 g of dried black walnut leaf. Cover and steep 10-15 minutes. Strain.
One cup, 2-3 times daily for internal use. For topical use (wash/compress): prepare a stronger infusion (4-6 g per 250 mL) and apply as a wash or soak.
2-3 times daily internally; as needed topically.
Topical use as needed. Internal use for short courses.
Topical use only under practitioner guidance.
Leaf infusion is milder than hull preparations and is used primarily as a topical astringent wash for skin conditions. This use is analogous to the German Commission E-approved use of J. regia leaf for mild skin inflammation. The infusion can be used as a sitz bath for hemorrhoids (prepare a larger volume) or as a gargle for mouth and gum inflammation.
Poultice
Strength: Fresh hull or powder paste applied topically
Apply crushed fresh green hull directly to the affected area, or make a paste from dried hull powder mixed with a small amount of water. Cover with gauze. For warts: apply a small piece of fresh hull directly to the wart, cover, and secure with adhesive bandage. Replace daily.
Apply to affected area 1-2 times daily.
1-2 times daily.
Until condition resolves or for 2-3 weeks.
Use with caution; avoid large areas. Patch test first.
Be aware that the hull will deeply stain skin, clothing, and bandages brown-black. The staining is cosmetically undesirable but not harmful and fades over days to weeks. For fungal skin infections and warts, the direct application of hull material is a traditional approach. Test on a small area first to check for skin sensitivity — juglone can be irritating to sensitive skin.
Safety & Interactions
Class 2a
Not to be used during pregnancy (AHPA Botanical Safety Handbook)
Contraindications
Black walnut hull is classified as AHPA Class 2a (not to be used during pregnancy). Juglone has demonstrated mutagenic and cytotoxic activity in vitro, and naphthoquinones as a class have potential developmental toxicity. The emmenagogue and uterine-stimulating properties attributed to some naphthoquinones provide an additional theoretical concern. No specific reproductive toxicity studies exist for black walnut hull in humans, but the precautionary principle applies strongly. Avoid all internal use during pregnancy.
Patients with documented allergy to walnuts (Juglans species) should avoid black walnut hull preparations. While the hull proteins differ from nut kernel allergens, cross-reactivity is possible. Anaphylactic reactions to walnut are well-documented (referring to the nut) — hull allergy is less characterized but caution is appropriate.
The strong tannin content and potential mucosal irritation from juglone make internal use inadvisable during active IBD flares (Crohn's disease, ulcerative colitis). The astringent and antimicrobial actions could further irritate an already inflamed and compromised intestinal mucosa.
Drug Interactions
| Drug / Class | Severity | Mechanism |
|---|---|---|
| Oral iron supplements (ferrous sulfate, ferrous gluconate) (Mineral supplements) | minor | The high tannin content of black walnut hull can chelate and precipitate iron and other minerals in the GI tract, reducing their absorption. |
| Laxatives and cathartic agents (Laxatives) | minor | Black walnut has mild laxative properties that could be additive with pharmaceutical laxatives. |
| Topical medications applied to the same skin area (Topical preparations) | minor | The tannin-rich, astringent nature of black walnut hull preparations may alter the absorption or efficacy of concurrently applied topical medications by forming a protein-tannin barrier on the skin surface. |
Pregnancy & Lactation
Pregnancy
unsafe
Lactation
insufficient data
PREGNANCY: Classified as AHPA Class 2a — not to be used during pregnancy. Juglone's mutagenic potential in vitro, cytotoxic activity, and the traditional attribution of emmenagogue properties to Juglans species all argue against use during pregnancy. No human reproductive safety data exist. Avoid all internal use during pregnancy. Topical use on small areas during pregnancy has not been specifically studied but is also generally advised against. LACTATION: Insufficient data. Whether juglone or its metabolites are excreted in breast milk is unknown. Given the cytotoxic and mutagenic properties of juglone in vitro, avoidance during lactation is prudent until safety data are available.
Adverse Effects
References
Monograph Sources
- [1] Gardner Z, McGuffin M (eds.). American Herbal Products Association's Botanical Safety Handbook, Second Edition: Juglans nigra. CRC Press, Boca Raton (2013)
- [2] Blumenthal M, Busse WR, Goldberg A, et al. (eds.). The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines (Juglandis folium). American Botanical Council, Austin, TX (1998)
Traditional Texts
- [3] Felter HW, Lloyd JU. King's American Dispensatory, 18th Edition: Juglans. Ohio Valley Co., Cincinnati (1898)
- [4] Hoffmann D. Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press, Rochester, VT (2003)
- [5] Clark HR. The Cure for All Diseases. New Century Press, Chula Vista, CA (1995)
- [6] Moerman DE. Native American Ethnobotany. Timber Press, Portland, OR (1998)
Last updated: 2026-03-23 | Status: published
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