Black walnut hulls (Juglans nigra)

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15. Safety

Red flags first.

• Pregnancy and breastfeeding: avoid. This is the Medicine position for this monograph. No human data exist for the hull in pregnancy or lactation; the evidence-based text on herbal medicines in pregnancy and lactation by Mills and colleagues has no entry for black walnut or Juglans [51]. Bascom lists black walnut among herbs that should not be taken in pregnancy [16]. The ARTG listing of MediHerb Wormwood Complex carries "Do not use if pregnant or likely to become pregnant" and "Do not use while breastfeeding" [9], but that product also contains wormwood, so the warning cannot be pinned on the hull. The single-herb hull capsule on the ARTG must carry a statement that pregnant or breastfeeding women seek professional advice before use [10]. MediHerb gives "professional supervision" for pregnancy and lactation, the entry it gives most herbs in its table, and no specific warning (pp. 30, 116) [5]. For the related walnut leaf, the HMPC does not recommend use in pregnancy and lactation for lack of data [24,48]. Juglone is cytotoxic, weakly genotoxic and a skin tumour promoter in animals (below), and the juglone content of a hull dose is unknown. Grade: precautionary; no human data.
• Liver. The TGA adverse event database holds two liver reports with products that contain black walnut: fulminant hepatitis with jaundice, ascites and fatty liver in 2005, with a 29-ingredient "cleanse" product as the sole suspected medicine, and liver injury in 2025, with an antiparasitic combination suspected together with paromomycin [49]. Both products held many other herbs, and the database records suspicion, not cause. No liver injury has been tied to the hull itself. Anyone who develops jaundice, dark urine, pale stools or pain under the right ribs while taking a hull product should stop it and needs prompt assessment. Grade: spontaneous reports, causality not established.
• Tree-nut allergy. The ARTG listing of a hull product carries "Contains tree nuts" [9], and the HMPC notes that allergic reactions should be considered in people allergic to the walnut family [24]. One Australian report describes itching of the lips and mouth, hives and facial swelling after an antiparasitic combination containing black walnut, taken with an oregano oil product; both were suspected [49]. Whether the hull carries the kernel allergens has not been measured. A person allergic to walnuts should avoid the hull. Grade: regulatory warning and one spontaneous report.
• Horses. Black walnut heartwood and wood shavings cause laminitis in horses, and an aqueous heartwood extract given by mouth is the standard experimental model of the disease [24,25]. Juglone itself inhibited equine neutrophil degranulation and oxygen radical release in vitro, and the authors concluded that juglone is not the trigger, at least through neutrophil activation [25]. The hull has not been implicated in the sources read. Hull residues and wood should still be kept away from horses. A case series of dogs that ate black walnut wood, nuts and hulls is being obtained in full text and is not used here.
• Children. No paediatric data and no sourced dose. For the related walnut leaf, even as a cutaneous preparation, the HMPC does not recommend use under 18 years [48]. Stearns gave doses to children in 1801 [11]; that is history, not guidance. Medicine position: not for children while there are no data. Grade: precautionary.

Adverse effects in people. No trial exists, so there are no trial-based adverse-effect data. Duke records "no side effects reported" from one source and the advice to limit use to a few weeks; he also gives "Class 2d", notes that juglone is mutagenic and, citing a secondary source, external carcinogenic effects after chronic use of J. regia (p. 101) [15]. Case reports of skin reactions and staining from black walnut hull juice are being obtained in full text. Hull juice stains skin brown-black; the stain resists washing and fades only as the skin renews (Figure 15b, J. regia) [38]. The Nature’s Sunshine listing carries the stimulant-laxative statement "Prolonged use may cause serious bowel problems" and "Do not use when abdominal pain, nausea or vomiting are present or if you develop diarrhoea" [10]. Those statements come with the laxative indication on the ARTG; whether the hull acts as a stimulant laxative has not been shown.

TGA adverse event reports (DAEN – medicines) [49]. Searched in September 2026 for "juglans", data to September 2026. Eight products containing J. nigra appear, every one a multi-ingredient product; no single-herb hull product has a report. A ninth hit, containing butternut (J. cinerea), was excluded.

TGA safety alerts, recalls and cancellations [50]. The TGA website was searched in September 2026 for "juglans", "black walnut", "juglone" and "walnut hull". No safety alert, advisory or recall names black walnut or juglone. One product, Hulda Herbs Fresh Green Hulls of Black Walnut Tincture (ARTG 56461), was cancelled at the sponsor’s request under section 30(1)(c) of the Therapeutic Goods Act 1989, effective 30/07/2021; the notice gives no safety reason. The TGA Database of Recalls, Product Alerts and Product Corrections was searched in October 2026 for "juglans", "black walnut", "walnut" and "juglone", for ARTG 91797 and 57518, and for the products named in the adverse event reports: no recall, product alert or product correction was found. That database searches product names and ARTG numbers, not ingredients, so a multi-herb product that contains the hull under another name would not show up through those terms [50].

Toxicology of juglone (HMPC review) [24].

These data come from pure juglone and from the leaf of J. regia. The HMPC’s comfort about dried leaf does not transfer automatically to a 60% ethanol extract of green hull, which is made to capture the naphthalene fraction before it oxidises (section 3.1). That gap is the main safety question for this drug.

Contraindications and cautions, each with its source and grade.

Herb–drug interactions. None documented for the hull in the sources read, and no interaction report was found in the TGA database [49]. MediHerb refers users to its own interaction chart, which is not held [5]. For the tannin-rich walnut leaf, the HMPC cites reports that walnut tannins may make alkaloids insoluble, reduce the absorption of other drugs and interfere with iron absorption (p. 25) [24]. Grade: theoretical, carried over from the leaf, with no hull-specific or clinical data. AIP comment (Medicine): taking the hull two hours apart from iron and from other oral medicines is a sensible precaution; it has not been tested.

Microbial and mould risk. A retail hull capsule grew fungi including Aspergillus sp. on culture [27], and fallen fruit lies on damp ground before hulling (section 3.1). Batch testing for moulds and aflatoxins is the practical control (section 10).

Older people. No data.

Overdose. No human case found. The HMPC reports none for walnut leaf [24].

Referral. Anyone considering black walnut hull, and especially anyone pregnant, breastfeeding, allergic to tree nuts or treating a child, should consult a degree-qualified herbalist with competencies and adequate training in pharmacognosy. Suspected worm infestation that persists, any blockage, severe abdominal pain or bleeding, and any sign of liver trouble need prompt assessment.