Skullcap

Scutellaria lateriflora

Family: Lamiaceae

Introduction

Skullcap, sometimes spelled scullcap, is a perennial in the mint family that grows to 3 feet and is native to the eastern United States.¹ It can be found in moist woodland areas throughout North America and its blue flowers appear from July through September.^1,2 The aerial (above-ground) parts of the plant are harvested during the flowering period and are used in herbal preparations in western herbal medicine. The root of an Asian species (S. baicalensis) is frequently employed in Traditional Chinese Medicine (TCM).¹

History and Cultural Significance

Skullcap’s genus name, Scutellaria, comes from the Latin scutella, a small dish or tray, which refers to the appearance of the sepals during the fruiting period.³ The species name, lateriflora, means “flowering on the side,” which is how the flowers appear on the one-sided racemes. Skullcap’s common name comes from the helmet-like shape of the flowers.³

Traditionally, the leaves of this herb were steeped to produce a tea or tonic.¹ Utilized by the Cherokee and other tribes of North America to promote menstruation, skullcap was employed in the ceremonial transition of young girls to womanhood.^1,2 The Cherokee also used infusions and decoctions of skullcap roots for treating diarrhea, kidney problems and breast pains, and to help expel the afterbirth.⁴ The Iroquois used an infusion of the powdered roots to prevent smallpox and to keep the throat clean.⁴ In North American folk medicine, skullcap was used as a sedative and nerve tonic, or “nervine,” and skullcap tea was drunk for anxiety.⁵

Due to its gentle relaxing effects, skullcap became a popular treatment in the 1700s for hydrophobia or rabies, resulting in one of its common names, mad-dog weed.^1,2,6 A Dr. Van Derveer (or Vandesveer) used skullcap to prevent and treat rabies in both humans and animals, claiming to have prevented 4,000 people and 1,000 cattle from being infected after having been bitten by rabid dogs.³ A number of scientists and doctors of the era questioned the validity of this treatment, and by 1852, the Eclectic physicans Drs. John King and Robert Newton had dismissed skullcap as a treatment for rabies.³

During the late 19^th and early 20^th centuries, the Eclectic physicians prescribed skullcap for nervousness caused by illness, teething, and mental or physical exhaustion; nervousness with muscular spasms; heart disorders of the nervous type with intermittent pulse; hysteria accompanied by uncontrollable muscular action; tremors; and subsultus tendinum (twitching of the tendons, notably the wrist, during low fevers).^7,8 King’s American Dispensatory also recommended skullcap for convulsions, delirium tremens, intermittent fever, neuralgia, tremors, and chorea (involuntary, rapid, jerky, forceful movements).⁸ The American Materia Medica, Therapeutics and Pharmacognosy includes the following additional uses for skullcap: twitching, nervous tics, epilepsy, paralysis agitans (a progressive, degenerative neurologic disease), and irritability and restlessness with nervous excitability and sleeplessness.⁹ Throughout the 20^th century and into the 21^st, American and Canadian herbalists and naturopaths continue to use skullcap as an effective antispasmodic, nervine tonic and sedative.³

Skullcap fluid extract was listed in the United States Pharmacopoeias from 1860 until 1900 and was included in the National Formulary from 1916-1942.³ The Health Canada Natural Health Products Directorate approved the oral traditional medicinal use of skullcap preparations equivalent to 0.25-12 g dried aerial parts per day to help relieve nervousness, as a sleep aid, and to help relieve the pain associated with menstruation.¹⁰ While not official, monographs published in both the British Herbal Pharmacopoeia (BHP) and the British Herbal Compendium (BHC) address S. lateriflora. The BHP lists skullcap as a mild sedative and the BHC recognizes the use of skullcap for nervous disorders due to anxiety, tension or stress; headaches; migraine; neurasthenia (a mental disorder characterized by chronic fatigue and concomitant physiologic symptoms); neuralgia; panic attacks; restlessness; sleep disorders; premenstrual tension and period pain; and to assist withdrawal from benzodiazepines.^11,12

Several cases of hepatotoxicity were attributed to skullcap in the late 1980s.¹³ Unfortunately, none of the multi-herb products implicated were tested to see if they actually contained skullcap.³ The herb germander (Teucrium canadense, Lamiaceae), also known as wood sage or wild basil, and the species in the wholesale herb trade known as pink skullcap (T. chamaedrys) are known hepatotoxins. They have been common skullcap adulterants for decades.^3,14 The toxicity in the case reports is associated with diterpenes that are contained in germander but not skullcap.³ This adulteration persists today and is addressed in the recent American Herbal Pharmacopoeia standards monograph on skullcap, along with questionable published research supposedly on S. lateriflora but actually done on inaccurately named species.³

Modern Research

While Western herbalists remain convinced that skullcap is an effective sedative, antispasmodic and nervine tonic, very little scientific research has been done on this species. One small singledose study was performed in 2003 on 19 healthy subjects. The effects were subjectively evaluated at 30, 60, 90 and 120 minutes after oral administration of one of 4 preparations: 1 capsule containing 350 mg of freeze-dried aerial parts of skullcap (Eclectic Institute, Sandy, OR); 1 capsule containing 100 mg of freezedried skullcap extract; 2 capsules containing 100 mg of freezedried skullcap extract; or 2 capsules of placebo. While there was little effect on cognition or overall energy, participants reported a noticeable decrease in anxiety.¹⁵ The value of this study is limited due to size, duration, subjective assessment scale used for measurement, and the fact that the participants were not suffering from anxiety, the condition being addressed in the study.^3,15

There are a small number of animal and in vitro studies on skullcap, none of which are conclusive in their results. One of the animal studies involved a combination product, so the efficacy of skullcap alone cannot be determined.¹⁶ Some pharmacological data suggest that the flavones in skullcap may be involved in its mechanism of action.³ Also, one animal study with very limited data suggests that skullcap may have some anti-inflammatory effects.³

Although there is more published research on the beneficial effects of preparations made from the root of Chinese skullcap (S. baicalensis), it would be unwise to assume that the same therapeutic effects are achievable with S. lateriflora. Clearly more scientific investigation is warranted on this species to support its well-established empirical evidence of efficacy and continued clinical use.

Future Outlook

Skullcap grows in the wild and commercial cultivation efforts have been developed.² One source estimates that 85% of the total 2001 harvest was from cultivated sources.¹⁷ While wild material in the United States is harvested sporadically throughout its native habitat, in 2001, approximately 70% of cultivated skullcap in the US market was imported from small growers outside of North America.¹⁷

Manufacturers of skullcap products who do not grow their own material should take care to ensure that the dried material they purchase is tested and correctly identified. Not only has S. lateriflora been adulterated with Teucrium species over the past decades, but more recent reports suggest that some seed stock sold as S. lateriflora may be another species entirely.³

Other than reports of the susceptibility of skullcap to 2 virus pathogens—tomato spotted wilt virus and another necrotic spot virus—major problems with diseases or insects have not been reported.^2,17 Ever-present threats to natural growth areas include urban growth and development. However, it is unclear what impact this population pressure may have on the production of skullcap.

—Gayle Engels

References

1. DerMarderosian A, Beutler JA, eds. The Review of Natural Products. 3rd ed. St. Louis, MO: Facts and Comparisons; 2002.

2. Joshee N, Patrick TS, Mentreddy RS, Yadav AK. Skullcap: Potential Medicinal Crop. Trends in New Crops and New Uses. Alexandria, VA: ASHS Press; 2002.

3. Upton R, ed. American Herbal Pharmacopoeia and Therapeutic Compendium: Skullcap Aerial Parts. Scotts Valley, CA: American Herbal Pharmacopoeia; 2009.

4. Moerman DE. Native American Ethnobotany. Portland, OR: Timber Press Inc.; 1998.

5. Foster S, Duke JA. A Field Guide to Medicinal Plants and Herbs: Eastern and Central North America. 2nd ed. Boston: Houghton Mifflin Co; 2000.

6. Foster S, Tyler VE. Tyler’s Honest Herbal. 4th ed. Binghamton, NY: Haworth Herbal Press; 1999.

7. Felter HW. The Eclectic Materia Medica, Pharmacology and Therapeutics. Cincinnati, OH: John K. Scudder; 1922. Available at: http://www.henriettesherbal.com/eclectic/felter/intro.html. Accessed June 1, 2009.

8. Felter HW, Lloyd JU. King’s American Dispensatory. Cincinnati, OH: Ohio Valley Co.; 1898. Available at: http://www.henriettesherbal.com/eclectic/kings/scutellaria.html. Accessed June 1, 2009.

9. Ellingwood F. The American Materia Medica, Therapeutics and Pharmacognosy. Evanston, IL: Ellingwood’s Therapeutist; 1919. Available at: http://www.henriettesherbal.com/eclectic/ ellingwood/index.html. Accessed June 1, 2009.

10. Health Canada Natural Health Products Directorate (NHPD). Skullcap. In: NHPD Compendium of Monographs. Ottawa, Ontario: Natural Health Products Directorate. January 18, 2008. Available at: http://www.hc-sc.gc.ca/dhp-mps/prodnatur/applications/licen-prod/monograph/mono_scullcap-scutellaire-eng.php. Accessed June 1, 2009.
11. British Herbal Medicine Association. British Herbal Pharmacopoeia. 4th ed. Exeter, UK: British Herbal Medicine Association; 1996.

12. Bradley P. British Herbal Compendium: A Handbook of Scientific Information on Widely Used Plant Drugs. Vol. 1. Bournemouth, UK: British Herbal Medicine Association; 2006.

13. DeSmet PSGM, Keller K, Hänsel R, Chandler RF, eds. Adverse Effects of Herbal Drugs. Vol. 3. Berlin: Springer Verlag; 1997.

14. Foster S. Scullcap substitution. HerbalGram. Fall 1985;3.
15. Wolfson P, Hoffmann DL. An investigation into the efficacy of Scutellaria lateriflora in healthy volunteers. Alternative Therapies in Health and Medicine. 2003;2:74-78.

16. Peredery O, Persinger MA. Herbal treatment following postseizure induction in rat by lithium pilocarpine: Scutellaria lateriflora (skullcap), Gelsemium serpervirens (gelsemium) and Datura stramonium (jimson weed) may prevent development of spontaneous seizures. Phytother Res. 2004;18:700-705. Cited by: Upton R, ed. American Herbal Pharmacopoeia and Therapeutic Compendium: Skullcap Aerial Parts. Scotts Valley, CA: American Herbal Pharmacopoeia; 2009.

17. Greenfield J, Davis JM. Medicinal Herb Production Guide: Skullcap (Scutellaria lateriflora L.). 2004. Natural Medicines of North Carolina Web site. Available at: http://www.naturalmedicinesofnc.org/Growers%20Guides/Skullcap-gg.pdf. Accessed June 2, 2009.