Black Walnut

What Is Black Walnut?

Black walnut is a large North American hardwood tree, prized for its timber and its strongly flavoured nuts. In herbal medicine the part used is the green hull, the thick fleshy coat around the developing nut, gathered while it is still unripe. The leaf and bark are used alongside it.

Juglans nigra grows wild across the eastern United States and southern Ontario, in rich woods and river valleys, and can reach 38 m ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. Native American peoples used its bark, hulls, leaves and roots as medicine and dye ^{33Reference 33Native American Ethnobotany Database (BR et al. · 1975Reviewhttp://naeb.brit.org/uses/search/?string=Juglans+nigraView study →}.

The green hull is rich in juglone, a naphthoquinone pigment that also occurs in the leaves, bark and roots ^{32Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. Herbalists use the hull as an astringent, a remedy for intestinal worms, and a topical treatment for fungal skin infections such as athlete’s foot and ringworm. Research has mostly been done on the kernel and on juglone in laboratory studies ^{9,10,22Reference 9Osztie et al. · 2024In vitroComprehensive Characterization of Phytochemical Composition, Membrane Permeability, and Antiproliferative Activity of Juglans nigra Polyphenols — in vitroView study →Reference 10Ho et al. · 2020In vitroProfiling Anticancer and Antioxidant Activities of Phenolic Compounds Present in Black Walnuts (Juglans nigra) Using a High-Throughput Screening Approach — in vitroView study →Reference 22Dos Santos Moreira et al. · 2021ReviewJuglone: A Versatile Natural Platform for Obtaining New Bioactive Compounds — reviewView study →}.

Black walnut is different from the English or Persian walnut (Juglans regia), the orchard walnut of Eurasia and the walnut of Chinese medicine ^{31Reference 31WhittemoreT., & Stone, DView study →}.

How Is Black Walnut Used?

The green hull is the main medicinal part. It is taken internally in short courses, with breaks between them, and applied to the skin.

• Green-hull tincture — the classic worming preparation, usually given in a formula with other herbs rather than alone.
• Hull salve or balm — applied to athlete’s foot, ringworm and other fungal skin complaints, and for sweaty hands and feet.
• Leaf liquid extract — taken as an astringent.
• Combinations — traditionally paired with ginger for griping, with dandelion root for skin eruptions, and with wormwood against intestinal parasites.

Traditional Uses

Native American Medicine

Black walnut was used by many Native American peoples, and different nations used different parts of the tree ^{33Reference 33Native American Ethnobotany Database (BR et al. · 1975Reviewhttp://naeb.brit.org/uses/search/?string=Juglans+nigraView study →}.

The green hulls and leaves were applied to the skin. The Delaware rubbed juice from the green hulls on ringworm, and the Comanche rubbed pulverised leaves on ringworm. The Houma washed “the itch” with an infusion of the nut shells, and the Cherokee washed sores with an infusion.

The bark was taken for the gut. The Meskwaki used the inner bark as a strong purge, the Iroquois took a bark decoction as a laxative, and the Rappahannock drank a root-bark infusion to prevent dysentery. The Kiowa took a decoction of the root bark to kill worms.

The Cherokee chewed the bark for toothache and noted that it was used cautiously because it is poisonous. The Iroquois applied the bark as a poultice for headache, and the Meskwaki applied charred bark to snakebite.

The nuts were an important food, and the bark, roots and hulls gave brown dye ^{32,33Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →Reference 33Native American Ethnobotany Database (BR et al. · 1975Reviewhttp://naeb.brit.org/uses/search/?string=Juglans+nigraView study →}.

Western Herbal Medicine

North American herbal practice uses the green hull of black walnut above all, with the leaf and bark alongside it. It is treated first as an astringent and second as a remedy for worms.

The hull is the classic worming preparation, usually given in a formula rather than alone. Applied to the skin, it is used for athlete’s foot, ringworm and excessive sweating of the hands and feet.

Herbalists and holistic veterinarians in British Columbia have recorded black walnut among the plants they use against intestinal worms in dogs, cats and pigs ^{26Reference 26Lans et al. · 2007ObservationalEthnoveterinary medicines used to treat endoparasites and stomach problems in pigs and pets in British Columbia, Canada — observational/ethnobotanicalView study →}.

Indications

• Intestinal worms [green hull; Western herbal medicine; root bark, Kiowa use] ⚠Caution: No study has tested a black walnut preparation against intestinal worms. Laboratory studies show juglone kills plant-parasitic nematodes ²⁹.
• Fungal skin infections, including athlete’s foot and ringworm [green hull or leaf, applied to the skin; Western herbal medicine, Native American use]
• Excessive sweating of the hands and feet [green hull, applied to the skin]
• Sores and itching skin [infusion used as a wash; Native American use]
• Constipation [inner bark; Meskwaki and Iroquois use]
• Diarrhoea and dysentery [root bark; Rappahannock use]
• Toothache [bark, chewed; Cherokee use]

Botany

Black walnut is a large deciduous tree in the walnut family (Juglandaceae), which also includes the hickories and pecan ^{31Reference 31WhittemoreT., & Stone, DView study →}. It usually grows to about 25 m, and can reach 38 m or more ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. In the forest it forms a long, straight trunk with a small, rounded crown. It has a deep taproot and several wide-spreading side roots ^{32Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

The bark is dark grey or brownish, and on mature trees it is split into narrow, rough, intersecting ridges ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

The leaves are pinnate, 20–60 cm long, with usually 15–19 lance-shaped, toothed leaflets, each 6–15 cm long. The leaflet at the tip is small or often missing ^{31Reference 31WhittemoreT., & Stone, DView study →}.

Male and female flowers grow on the same tree. The male flowers hang in catkins 5–10 cm long, and flowering comes in spring ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

The fruit is round, 3.5–8 cm across, with a thick green husk that is warty and glandular. The husk develops from the flower’s outer parts rather than the fruit wall, so the walnut itself is botanically a nut ^{31Reference 31WhittemoreT., & Stone, DView study →}. Inside is a round nut 3–4 cm across, with a hard shell that is very deeply grooved. The fruit ripens in September or October and falls soon after the leaves ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

Juglone occurs in the leaves, bark, nut husks and roots. It suppresses the growth of many garden vegetables and some conifers planted near the tree ^{32Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

English walnut (J. regia) is easy to tell apart. It has 5–11 broad leaflets with smooth edges, and a thin, wrinkled shell without deep grooves ^{31Reference 31WhittemoreT., & Stone, DView study →}.

Distribution

Black walnut grows throughout the eastern United States, north to southern Minnesota, Wisconsin, Michigan and southern Ontario, and south to northwestern Florida and Louisiana. Scattered populations reach west to eastern Texas, Oklahoma, Kansas and southeastern South Dakota ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}.

It grows in rich woods from sea level to about 1,000 m, and does best on deep, moist, fertile soils such as alluvial bottomlands and coves ^{31,32Reference 31WhittemoreT., & Stone, DView study →Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. It is widely planted as an ornamental and for its nuts ^{31Reference 31WhittemoreT., & Stone, DView study →}.

Growing Conditions

Cultivation snapshot for Black Walnut

LifeperennialZoneUSDA 4–9

• A large, long-lived deciduous tree (often 75–100 ft), so give it plenty of open space and full sun.
• Prefers deep, rich, moist but well-drained soil, as found in bottomlands and stream valleys.
• Cold-hardy across roughly USDA zones 4–9.
• Strongly allelopathic: its roots release juglone, which stunts or kills many sensitive plants (tomatoes, peppers, blueberries, rhododendrons and more) within and beyond its drip line — do not plant these nearby.

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Pharmacology & Research

Research on Juglans nigra is small and almost entirely preclinical. Since about 2018 a number of laboratory and rodent studies have looked at the kernel, the hull and the leaf, alongside a larger literature on juglone itself.

Most of the strongest findings were measured in the kernel, the edible nut, rather than the green hull used in herbal medicine. The diabetes, liver and kernel-oil “walnut” studies that fill much of PubMed were done on other species, mostly J. regia.

No therapeutic human trial of black walnut has been published. The one registered J. nigra study compared blood responses to black-walnut, English-walnut and butter breakfasts in healthy adults (NCT04849949) ^{30Reference 30Black Walnuts et al.RCThttps://clinicaltrials.gov/study/NCT04849949View study →}.

1. Antioxidant

This activity has been measured in the medicinal parts as well as the kernel. Supercritical-CO₂ extracts of the green husk showed radical-scavenging capacity by FRAP, DPPH and total-phenolic assays, and husk that had not been dried scored about twice as high as dried husk ^{12Reference 12Wenzel et al. · 2017In vitroAntioxidant potential of Juglans nigra, black walnut, husks extracted using supercritical carbon dioxide with an ethanol modifier — in vitroView study →}.

Ethanolic leaf and green-husk extracts were strongly antioxidant. At 4 µg/mL they reduced micronucleus formation in stimulated human lymphocytes by 58% and 65% respectively. The extracts contained 103 identified compounds ^{13Reference 13Rajković et al. · 2024In vitroChemical Composition and Protective Possibilities of Juglans nigra Leaves and Green Husks Extracts: DNA Binding and Micronucleus Assay in Human Lymphocytes — in vitroView study →}.

A high-throughput screen of kernel phenolics found several, including quercetin, epicatechin gallate and penta-O-galloyl-glucose, with antioxidant capacity higher than the Trolox control ^{10Reference 10Ho et al. · 2020In vitroProfiling Anticancer and Antioxidant Activities of Phenolic Compounds Present in Black Walnuts (Juglans nigra) Using a High-Throughput Screening Approach — in vitroView study →}.

Every measurement is a chemical or cell-based assay. No study has tested an antioxidant outcome in an animal or a person.

2. Anticancer / Antiproliferative

Three independent in vitro studies point the same way. Polyphenol profiling of J. nigra bark, leaf and pericarp identified 161 compounds, and eight were isolated from the pericarp. Of these, juglone inhibited the growth of all three human cancer cell lines tested, with activity similar to the clinical standards. Permeability testing suggested juglone can cross gut and blood–brain-barrier membranes by passive diffusion ^{9Reference 9Osztie et al. · 2024In vitroComprehensive Characterization of Phytochemical Composition, Membrane Permeability, and Antiproliferative Activity of Juglans nigra Polyphenols — in vitroView study →}.

A screen of 12 ellagic-acid-rich plants found black walnut among the richest in active compounds. Its extract was most effective against renal (Caki-1) and colorectal (HCT116) cancer cells ^{11Reference 11Armonavičius et al. · 2025In vitroEvaluation of the Anticancer Activity of Medicinal Plants Predominantly Accumulating Ellagic Acid Compounds — in vitroView study →}.

In the kernel-phenolic screen, penta-O-galloyl-glucose and quercetin-3-glucoside slowed the growth of lung cancer cells, and also of normal lung fibroblasts ^{10Reference 10Ho et al. · 2020In vitroProfiling Anticancer and Antioxidant Activities of Phenolic Compounds Present in Black Walnuts (Juglans nigra) Using a High-Throughput Screening Approach — in vitroView study →}.

All of this is cell-line work. There is no J. nigra animal tumour model.

Gap: no in vivo cancer model and no selectivity data separating tumour-cell killing from general cytotoxicity — the same naphthoquinone chemistry drives both.

3. Antibacterial

Most of the antibacterial evidence is on the kernel. Isolated juglone, the main compound of the hull, damages bacterial membranes and has an MIC of 15.6 µg/mL against E. coli, S. aureus and Salmonella pullorum ^{24Reference 24Wang et al. · 2025In vitroAntimicrobial activity and possible mechanisms of juglone against Escherichia coli, Staphylococcus aureus, and Salmonella pullorum — in vitroView study →}.

Bioassay-guided work on 22 kernel cultivars found four with activity against Staphylococcus aureus. It identified glansreginin A, azelaic acid, quercetin and eriodictyol-7-O-glucoside among the active compounds ^{15Reference 15Ho et al. · 2018In vitroIdentifying Antibacterial Compounds in Black Walnuts (Juglans nigra) Using a Metabolomics Approach — in vitroView study →}.

Glansreginin A was later measured across 12 cultivars at 6.8–47 mg/kg. It had moderate activity against S. aureus and Bacillus anthracis but no antioxidant or anticancer effect ^{16Reference 16Ho et al. · 2023In vitroQuantification and characterization of biological activities of glansreginin A in black walnuts (Juglans nigra) — in vitroView study →}.

A tannin fraction from J. nigra inhibited Listeria monocytogenes at 62.5–125 µg/mL ^{17Reference 17Amarowicz et al. · 2008In vitroAntibacterial activity of tannin constituents from Phaseolus vulgaris, Fagopyrum esculentum, Corylus avellana and Juglans nigra — in vitroView study →}.

Two whole-extract screens are closer to herbal practice. Black walnut was one of seven botanicals with good activity against stationary-phase (persister) Borrelia burgdorferi in vitro, although its MIC against growing Borrelia was high ^{18Reference 18Feng et al. · 2020In vitroEvaluation of Natural and Botanical Medicines for Activity Against Growing and Non-growing Forms of B. burgdorferi — in vitroView study →}. It also showed broad activity against microbes from human and canine wounds ^{19Reference 19Detering et al. · 2025In vitroIn vitro characterization of potential botanicals to reduce infection and improve the rate of wound healing in humans and canines — in vitroView study →}.

The concentrations are high, and no study shows that a green-hull preparation reaches antibacterial levels in the body.

4. Hepatoprotective

This rests on one in vivo study. Rats were given sodium arsenite for five weeks, with or without J. nigra at 100 mg/kg. Black walnut reduced the rise in liver enzymes, lessened liver damage on histology, and cut micronucleus formation by 50%. It did not protect sperm count or motility ^{20Reference 20Owumi et al. · 2013AnimalProtective effect of Juglans nigra on sodium arsenite-induced toxicity in rats — animal model (in vivo)View study →}.

Leaf and husk extracts also protected human lymphocytes from chromosome damage in vitro ^{13Reference 13Rajković et al. · 2024In vitroChemical Composition and Protective Possibilities of Juglans nigra Leaves and Green Husks Extracts: DNA Binding and Micronucleus Assay in Human Lymphocytes — in vitroView study →}.

That is one rodent study in one chemical-injury model, with no replication and no dose-response.

5. Anti-Inflammatory

One in vitro study supports this. Methanolic kernel extracts of five black walnut cultivars were tested on LPS-stimulated human U-937 cells. Two cultivars, Surprise and Sparrow, inhibited all six detected cytokines when added before the LPS. The other three had weak or no effects, and no extract worked when added after the LPS. None was toxic to the cells ^{14Reference 14Ho et al. · 2019In vitroBlack Walnut (Juglans nigra) Extracts Inhibit Proinflammatory Cytokine Production From Lipopolysaccharide-Stimulated Human Promonocytic Cell Line U-937 — in vitroView study →}.

That is one cell-line study on the kernel, with no animal or human data.

6. Antifungal

Antifungal use for athlete’s foot, ringworm and other skin infections is one of black walnut’s main traditional applications. No antifungal study of a J. nigra preparation was located.

The support is at the level of the compound. Juglone inhibits Candida albicans growth (MIC 15.6 µg/mL), and it suppresses hyphal formation and early biofilm formation by disrupting the yeast’s redox balance ^{23Reference 23Obeidat et al. · 2026In vitroJuglone suppresses morphogenesis and early biofilm formation in Candida albicans through disruption of oxidative homeostasis — in vitroView study →}. Reviews list antifungal activity among juglone’s characterised actions ^{22Reference 22Dos Santos Moreira et al. · 2021ReviewJuglone: A Versatile Natural Platform for Obtaining New Bioactive Compounds — reviewView study →}.

Gap: no antifungal test of an actual black-walnut preparation against a clinical fungus; the case is built entirely on isolated-juglone data plus tradition.

7. Antiparasitic / Anthelmintic

The green hull’s use against worms is the herb’s best-known application, and juglone is most concentrated in the green, unripe hull. No controlled study of J. nigra against a human or veterinary parasite was located.

Black walnut is recorded in ethnoveterinary practice for intestinal worms in pets and pigs ^{26Reference 26Lans et al. · 2007ObservationalEthnoveterinary medicines used to treat endoparasites and stomach problems in pigs and pets in British Columbia, Canada — observational/ethnobotanicalView study →}, and the Kiowa took a root-bark decoction to kill worms ^{33Reference 33Native American Ethnobotany Database (BR et al. · 1975Reviewhttp://naeb.brit.org/uses/search/?string=Juglans+nigraView study →}. In the laboratory, juglone and synthetic derivatives of it kill plant-parasitic nematodes by increasing oxidative damage ^{29Reference 29Guo et al. · 2026In vitroDiscovery of juglone derivatives as potential nematicides by exacerbating oxidative damage — in vitroView study →}, and reviews list antiparasitic activity among juglone’s actions ^{22Reference 22Dos Santos Moreira et al. · 2021ReviewJuglone: A Versatile Natural Platform for Obtaining New Bioactive Compounds — reviewView study →}.

Gap: no efficacy study of black walnut against any human or animal parasite; the juglone evidence is on plant nematodes and modified derivatives, a considerable extrapolation from the whole-hull remedy.

Mechanisms

Juglone is a naphthoquinone that cycles between oxidised and reduced forms and generates reactive oxygen species. It has been studied for its activity against fungi, bacteria, nematodes and cancer cells, all in laboratory models.

The phenolic fraction (tannins, ellagic acid, gallic acid and flavonoids) has been studied for its antioxidant and antibacterial activity, mostly in the kernel.

Clinical Trials

The one completed human study of black walnut is a dietary study of the nut as a food ^{30Reference 30Black Walnuts et al.RCThttps://clinicaltrials.gov/study/NCT04849949View study →}.

Last checked: February 2025.

Two other J. nigra findings have not been followed up. A 2025 rat study gave black-walnut kernel oil to rats with drug-induced hypothyroidism ^{21Reference 21Morakabati et al. · 2025AnimalThe Impact of Black Walnut (Juglans nigra) Oil on Male Wistar Rats Suffering from Methimazole-Induced Hypothyroidism — animal model (in vivo)View study →}. A 1961 study found that an extract of unripe hulls depressed movement in animals from water fleas to rabbits, and identified juglone as the active compound ^{25Reference 25Westfall et al. · 1961Depressant agent from walnut hulls — animalView study →}.

Phytochemistry

The green hull’s signature compound is juglone (5-hydroxy-1,4-naphthoquinone). It occurs in the leaves, bark, nut husks and roots, and is highest in the green, unripe hull ^{32Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. It is present in the bark and nuts but not in the heartwood ^{27Reference 27Minnick et al. · 1987AnimalThe induction of equine laminitis with an aqueous extract of the heartwood of black walnut (Juglans nigra) — animal model (in vivo)View study →}. In English walnut, juglone measured about 21–43 mg per 100 g of green husk and 5–23 mg per 100 g of leaf ^{8Reference 8Cosmulescu et al. · 2011Juglone Content in Leaf and Green Husk of Five Walnut (Juglans regia L.) CultivarsView study →}.

The bark, leaf and pericarp carry a large phenolic load. A 2024 analysis of J. nigra identified 161 compounds in these parts. From the pericarp it isolated juglone, ellagic acid, gallic acid, ethyl gallate, myricetin-3-O-rhamnoside and two quercetin glycosides ^{9Reference 9Osztie et al. · 2024In vitroComprehensive Characterization of Phytochemical Composition, Membrane Permeability, and Antiproliferative Activity of Juglans nigra Polyphenols — in vitroView study →}. A separate analysis found 103 compounds in leaf and green-husk extracts ^{13Reference 13Rajković et al. · 2024In vitroChemical Composition and Protective Possibilities of Juglans nigra Leaves and Green Husks Extracts: DNA Binding and Micronucleus Assay in Human Lymphocytes — in vitroView study →}. The bark is rich in tannins.

The kernel has a different profile. Its phenolics include penta-O-galloyl-glucose, epicatechin gallate and quercetin ^{10Reference 10Ho et al. · 2020In vitroProfiling Anticancer and Antioxidant Activities of Phenolic Compounds Present in Black Walnuts (Juglans nigra) Using a High-Throughput Screening Approach — in vitroView study →}, along with glansreginin A, azelaic acid and eriodictyol-7-O-glucoside ^{15,16Reference 15Ho et al. · 2018In vitroIdentifying Antibacterial Compounds in Black Walnuts (Juglans nigra) Using a Metabolomics Approach — in vitroView study →Reference 16Ho et al. · 2023In vitroQuantification and characterization of biological activities of glansreginin A in black walnuts (Juglans nigra) — in vitroView study →}. Black walnut kernels are about 60% fat and 29% protein by dry weight ^{32Reference 32Coladonato · 1991Juglans nigra, black walnut — distribution, site characteristics, botanical description, juglone, nut composition and wildlife value — species databaseView study →}. Walnut kernels also contain serotonin and its methylated relative Nω-methylserotonin.

The leaf has an aromatic volatile oil. Headspace analysis of walnut-family leaves found β-pinene, β-caryophyllene, α-pinene, germacrene D and limonene ^{4Reference 4Farag MA · 2008Headspace analysis of volatile compounds in leaves from the Juglandaceae (walnut) family}. A walnut-leaf hydrosol contained homoveratrole, piperitone, thymol, carvacrol, eugenol, γ-eudesmol and nonadecane ^{1Reference 1Moravej et al. · 2016Chemical Composition and the Effect of Walnut Hydrosol in Glycemic Control of Type 1 Diabetic PatientsView study →}.

The juglone amounts, the fatty-acid figures and the leaf-oil analyses come from English walnut or from the walnut family in general, not from black walnut itself ^{1,4,7,8Reference 1Moravej et al. · 2016Chemical Composition and the Effect of Walnut Hydrosol in Glycemic Control of Type 1 Diabetic PatientsView study →Reference 4Farag MA · 2008Headspace analysis of volatile compounds in leaves from the Juglandaceae (walnut) familyReference 7Poggetti et al. · 2018Kernel oil content and oil composition in walnut (Juglans regia L.) accessions from north-eastern ItalyView study →Reference 8Cosmulescu et al. · 2011Juglone Content in Leaf and Green Husk of Five Walnut (Juglans regia L.) CultivarsView study →}.

Constituent Summary

Amounts cited to ^{7Reference 7Poggetti et al. · 2018Kernel oil content and oil composition in walnut (Juglans regia L.) accessions from north-eastern ItalyView study →} and ^{8Reference 8Cosmulescu et al. · 2011Juglone Content in Leaf and Green Husk of Five Walnut (Juglans regia L.) CultivarsView study →} were measured in English walnut (Juglans regia).

Dosage

The only doses studied come from animal and cell experiments, and from one dietary study of the nut.

Traditional Dosage

Courses are traditionally short, with breaks between them.

Safety & Pregnancy

Black walnut is best kept to short courses. The green hull is rich in juglone, a reactive compound that is toxic to cells in laboratory studies ^{9,22Reference 9Osztie et al. · 2024In vitroComprehensive Characterization of Phytochemical Composition, Membrane Permeability, and Antiproliferative Activity of Juglans nigra Polyphenols — in vitroView study →Reference 22Dos Santos Moreira et al. · 2021ReviewJuglone: A Versatile Natural Platform for Obtaining New Bioactive Compounds — reviewView study →}. Wood and bark extracts are toxic to horses.

Full Safety & Interactions Detail

No human safety study. No human safety, toxicology or drug-interaction study of Juglans nigra has been done, and dosing guidance is traditional. Anyone with a tree-nut allergy should avoid it.

Juglone. Juglone is a redox-active naphthoquinone that binds DNA and is toxic to cells in laboratory studies ^{22Reference 22Dos Santos Moreira et al. · 2021ReviewJuglone: A Versatile Natural Platform for Obtaining New Bioactive Compounds — reviewView study →}. At low concentrations, leaf and green-husk extracts protected human lymphocytes from chromosome damage, cutting micronucleus formation by 58–65% at 4 µg/mL ^{13Reference 13Rajković et al. · 2024In vitroChemical Composition and Protective Possibilities of Juglans nigra Leaves and Green Husks Extracts: DNA Binding and Micronucleus Assay in Human Lymphocytes — in vitroView study →}.

Horses. A water extract of black walnut heartwood, given by stomach tube, caused Obel grade 3–4 laminitis in eight of ten horses within 12 hours ^{27,28Reference 27Minnick et al. · 1987AnimalThe induction of equine laminitis with an aqueous extract of the heartwood of black walnut (Juglans nigra) — animal model (in vivo)View study →Reference 28Eaton et al. · 1995AnimalDigital Starling forces and hemodynamics during early laminitis induced by an aqueous extract of black walnut (Juglans nigra) in horses — animal model (in vivo)View study →}. Juglone was found in the bark and nuts but not in the heartwood, so the laminitis is caused by a different compound ^{27Reference 27Minnick et al. · 1987AnimalThe induction of equine laminitis with an aqueous extract of the heartwood of black walnut (Juglans nigra) — animal model (in vivo)View study →}. Green hulls are also a hazard to dogs.

References

1. Moravej, H., Salehi, A., Razavi, Z., Moein, M. R., Etemadfard, H., Karami, F., & Ghahremani, F. (2016). Chemical Composition and the Effect of Walnut Hydrosol in Glycemic Control of Type 1 Diabetic Patients. Int J Endocrinol Metab, 14(1). doi:10.5812/ijem.34726
2. Amaral JS, Seabra RM, Andrade PB, Valentao P, Pereira JA, Ferreres F. (2004). Phenolic profile in the quality control of walnut (Juglans regia L.) leaves. Food Chem Toxicol. 88(3):373–9.
3. Culpeper, N. (1995). Culpeper’s complete herbal: A book of natural remedies for ancient ills. Ware, Denmark: Wordsworth Editions.
4. Farag MA. (2008). Headspace analysis of volatile compounds in leaves from the Juglandaceae (walnut) family. J Essent Oil Res. 20(4):323–7.
5. Ma, S., Huang, D., Zhai, M., Yang, L., Peng, S., Chen, C., Xu, M. (2015). Isolation of a novel bio-peptide from walnut residual protein inducing apoptosis and autophagy on cancer cells. BMC Complementary and Alternative Medicine, 15(1). doi:10.1186/s12906-015-0940-9
6. Wu, J. N. (2005). An illustrated Chinese materia medica. New York: Oxford University Press. (Pg. 364-365).
7. Poggetti, L., Ferfuia, C., Chiabà, C., Testolin, R., & Baldini, M. (2018). Kernel oil content and oil composition in walnut (Juglans regia L.) accessions from north-eastern Italy. Journal of the Science of Food and Agriculture, 98(3), 955-962. doi:10.1002/jsfa.8542
8. Cosmulescu, S. N., Trandafir, I., Achim, G., & Baciu, A. (2011). Juglone Content in Leaf and Green Husk of Five Walnut (Juglans regia L.) Cultivars. Notulae Botanicae Horti Agrobotanici Cluj-Napoca, 39(1), 237-240. doi:10.15835/nbha3915728
9. Osztie, R., et al. (2024). Comprehensive Characterization of Phytochemical Composition, Membrane Permeability, and Antiproliferative Activity of Juglans nigra Polyphenols — in vitro. Int J Mol Sci. https://pubmed.ncbi.nlm.nih.gov/39000038/
10. Ho, K. V., et al. (2020). Profiling Anticancer and Antioxidant Activities of Phenolic Compounds Present in Black Walnuts (Juglans nigra) Using a High-Throughput Screening Approach — in vitro. Molecules. https://pubmed.ncbi.nlm.nih.gov/33023106/
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