Black walnut (1)
Leaf and bark (2, 3, 5);
Green hull (2, 4), yellow skin of inner nut, and oil of ripe kernel (2).
Native to North America, Juglans nigra is a monoecious tree with unisexual flowers (2, 6). The bark is rough and chunky (6). Black walnut grows up to 30 metres high (6) with a trunk diameter of up to 1.8 metres (1).The canopy is formed by deciduous pinnate leaves with a paler underside (2) and the round green fruit is 5-7cm across (6).
The wood was valued for making wagons, wagon wheels, wainscoting, gunstocks, and furniture. Leaves and husks were used for dyeing, and the oil was used for burning in lamps, wood polish, paint additive, and eaten as butter (2).
A type of naphthoquinone called juglone (3-5, 7) a constituent also found in J. regia, a species used in a medicinally similar way to black walnut and more frequently. The extract of bark and rind was found to contain 45% tannin (8).
As very little research has been conducted actions are based on traditional use.
Black walnut has been used as a laxative (2, 5, 9) and despite such a high tannin content the powdered bark is claimed to be a purgative (2). Anthelmintic actions (1, 4, 5, 7) have long been known traditionally, and its alterative properties (2, 4, 7, 9) are employed to treat various skin conditions. Black walnut anti-viral (HSV 1) action has been known for over 100 years (5, 1).
Little research has been done on J. nigra, however more is known about J. regia which is more commonly used. It is conjecture as to whether the information known about J. regia is applicable to J. nigra. Juglone is considered the major active constituent in both plants (10). Juglone has mutagenicity in animals (3) however other in vivo research showed a reduction in tumour growth rate in mice treated with juglone derived from J. nigra (11). Research investigating laminitis in horses showed that J. nigra heartwood causes laminitis but juglone was not the causative agent as it not a constituent found in the wood (12). In vitro research using black walnut husk extract showed anti-fungal activity as well as antibacterial action against several strains of bacteria including Escherichia coli & Staphylococcus aureus (13).
There are no known clinical trials to date.
Intestinal worms (1, 2, 4, 5, 7); skin conditions including eczema (1, 2, 4, 7) (used both internally and externally)(2), and herpes (1, 2, 5, 7). Grieve mentions that both the unripe fruit and the juice from husks can be used for sore throat (2).
There is very little information available for any recommendations.
Contact dermatitis from the bark has been reported (14). Long term external use of J. regia has been linked to carcinogenesis which may or may not be applicable to J. nigra (3).
Infusion: add 0.5 litre boiling water 30g dried bark or leaf and leave stand for 6 hours before drinking approximately 200ml tds (2), used internally or externally.
Liquid extract: 1.5 – 5.5ml/day of a 1:2 extract of green hulls (7).
Oil from ripe kernels can be used externally for wounds and gangrene (2).
1. King's American Dispensatory. Henriette's Herbal. 1999-2008. Henriette Kress. Accessed 15 September 2008.
2. Grieve M. 1980. A Modern Herbal. London: Penguin Books
3. McGuffin M, Hobbs C, Goldberg A (eds). 1997. Botanical Safety Handbook. American Herbal Products Association.
4. Bone K. 2007. The Ultimate Herbal Compendium: a Desktop Guide for Herbal Prescribers. Warwick, Qld. : Phytotherapy Press.
5. Hoffman D. 2003. Medical Herbalism. Rochester, Vt: Healing Arts Press.
6. Black walnut. Department of Forestry College of Natural Resources. 2008. Virgin Tech Forestry Department.USA. Accessed 11 September 2008.
7. Mills S, Bone K. 2005. The Essential Guide to Herbal Safety. St. Louis, Mo: Elsevier Churchill Livingstone.
8. Brinker F. 1997. Herb Contraindications and Drug Interactions. Oregon: Eclectic Institute Inc.
9. Mills S, Bone K. 2000. Principles and Practice of Phytotherapy. Edinburgh: Churchill Livingstone.
10. Yarnell E, Abascal K, Hooper CG. 2003. Clinical Botanical Medicine. Mary Ann Liebert: Larchmont, NY.
11. Bhargava UC, Westfall BA. Antitumor activity of Juglans nigra (black walnut) extractives. Journal of Pharmaceutical Sciences 1968; 57 (10): 1674-1677. (Abstract online). Available:
12. Minnick PD, Brown CM, BraeseltonWE, Meerdink GL, Slander MR. The induction of equine laminitis with an aqueous extract of the heartwood of black walnut (Juglans nigra) Veterinary and Human Toxicology (Vet Hum Toxicol) 1987; 29 (3): 230-233. (Abstract online). Available EBSCO/Medline. (26 August 2008)
13. Heisey RM, Gorham BK. Antimicrobial effects of plant extracts on Streptococcus mutans, Candida albicans, Trichophyton rubrum and other micro-organisms. Letters in Applied Microbiology 1992;14:136-139.
14. Craton DW, Williams RD. Juglone dermatitis: allergy or irritant? 1981;90:98-102. (Abstract online). Available: CAB Direct. (26 August 2008)
This monograph was authored in 2008 by Lisa Marina Kelly, a student in Southern Cross University's Bachelor of Naturopathy programme, and edited by Nena Aleschewski BNat. While the author and editor have strived to cite published information accurately, Southern Cross University will not be responsible for any inaccuracies that may have occurred.
This information is provided for educational purposes only and does not constitute medical advice. If you wish to use herbal medicine as part of your health care, seek the advice of an appropriately qualified practitioner.
Updated: 16 October 2012