Adulteration of Skullcap (Scutellaria lateriflora)
By Stefan Gafner, PhD* and Mark
Blumenthal
American Botanical Council, PO Box 144345,
Austin, TX 78714
*Corresponding
author: email
Keywords:
Scutellaria
lateriflora, skullcap
herb, adulterant, adulteration
Goal: The goal of this bulletin is to
provide timely information and/or updates on issues of adulteration of Scutellaria lateriflora to the international
herbal products industry and extended natural products community in general. It
is intended to complement the previously published works regarding skullcap
adulteration, e.g., the American Herbal
Pharmacopoeia Skullcap Monograph published by Upton et al.1
and the article by Foster in HerbalGram,2 by presenting
new data on the occurrence of adulteration, the market situation, and
consequences for the consumer and the industry.
1
General Information
1.1
Common name: Skullcap3
1.2
Other common names:
English: Blue skullcap, helmet flower,
hoodwort, European or greater skullcap, Quaker bonnet, mad-dog skullcap, mad
weed, scullcap, Virginia skullcap4
French: Scutellaire, scutellaire latériflore,
scutellaire de Virginie, toque, toque casquée5
German: Helmkraut, seitenblütiges Helmkraut5
Italian: Scutellaria
Spanish: Escutelaria, escutelaria de Virginia
1.3
Accepted Latin binomial: Scutellaria lateriflora6,7
1.4
Synonyms: Cassida lateriflora; Scutellaria polybotrya6,7
1.5
Botanical family:
Lamiaceae (formerly Labiatae)
1.6
Plant part and form:
The flowering aerial parts of S.
lateriflora are used fresh, or dried as an infusion, as a tincture, or in the
form of a fluid extract.1 Suggested daily dosages vary,
depending on the author, and correspond to 0.25-12 g of dried aboveground flowering
parts.1,8,9
1.7
General use(s): Traditionally,
skullcap is used to help relieve nervousness and anxiety, as a sleep aid
(mainly for stress-related cases of insomnia), or as an antispasmodic.1,7,8
2 Market
2.1
Importance in the trade:
Skullcap is not a widely traded botanical commodity. In 2001, approximately 16
tons (35,000 pounds) of material were reportedly harvested and sold worldwide.10
No statistics on more recent volumes of harvested skullcap material could be
identified in the published literature. The limited
popularity of the herb is also shown by recent sales data from the United
States (Table1), where it ranked between #99 and #107 of all single herbal
dietary supplements in the Natural retail channel, and between #149 and #157 in
the Mainstream Multi-Outlet retail channel. (T. Smith e-mail to S. Gafner, September
2, 2015 and September 3, 2015)
Table 1: Sales data for skullcap dietary
supplements from 2012-2014.
Channel
|
2012
|
2013
|
2014
|
|
Rank
|
Sales [US$]
|
Rank
|
Sales [US$]
|
Rank
|
Sales [US$]
|
Naturala
|
107
|
556,856
|
106
|
577,065
|
99
|
625,734
|
Mainstream Multi-Outletb
|
n/a
|
19,355
|
157
|
22,735
|
149
|
27,997
|
aAccording
to SPINS (SPINS
does not track Whole Foods Market sales, which is a major natural products
retailer in the US)
bAccording to SPINS/IRI
(the Mainstream Multi-Outlet channel was formerly known as food, drug and mass
market channel [FDM], exclusive of possible sales at Walmart)
n/a: not available
Source: T. Smith (American
Botanical Council) e-mail September 2, 2015 and September 3, 2015
2.2
Supply sources: Most
supplies on the North American market appear to be obtained from cultivated
sources both in the United States (e.g., Minnesota, Missouri, North Carolina,
Oregon, and Washington) and internationally (e.g., Chile, Costa Rica, and Mexico).11
According to a report for the Australian government, Australian growers formerly
supplied skullcap, but production halted after 2003 when global prices dropped
and local growers were not able to compete with the prices from abroad.12
The majority of the skullcap used in products sold in Australia is now imported
(H. Wohlmuth e-mail to S. Gafner, January 19, 2015). There is some commercial
material available that is harvested in the wild in North America, but the
majority (85% according to a report from 2001) is obtained from cultivation.10
2.3
Raw material forms: In
the United States, many companies that manufacture products containing properly
authenticated skullcap grow it themselves.11 Bulk skullcap raw
material is mainly sold as cut and sifted, in form of a teabag cut, or as
powdered aboveground parts, which may be more susceptible to adulteration,
since the distinct features for macroscopic identification are no longer
recognizable.
2.4 Market dynamics: In 2001, an estimated 16 tons of
skullcap were harvested and sold on world markets at a price of US $9-13/kg.10
Since the cessation of production in Australia, prices for imported skullcap
from North America have been gradually increasing and reached Australian (AUD) $42/kg
(US $31/kg based on the exchange rate from June 1, 2006) for organic crops and
AUD 25-30/kg (US $19-22/kg) for conventional crops in 2006.12 Based
on a 2008 newsletter of the Australian raw material supplier Network Nutrition,
growers in the United States have experienced issues with cultivation due to
difficulties with seed germination, crop failure, and various other issues.
This has led to a shortage in raw material and the appearance of material where
skullcap was substituted with other species of Scutellaria.13 In recent years, the demand for skullcap
has been has been subject to fluctuations but overall trended flat or was slightly
increasing. Currently, growers under contract can obtain between US $18-19/kg
for conventional and US $24-29/kg for certified organic skullcap (E. Fletcher e-mail
to S. Gafner, January 20, 2015; L. Ballard oral communication to S. Gafner,
January 28, 2015). Pricing for the consumer is in the range of US $43-47/kg for
conventionally-grown herb and US $70-110/kg for organically grown skullcap,
according to an informal survey, by a co-author of this Bulletin (SG), of
smaller companies that had listed pricing on the Internet.
3 Adulteration
3.1
Known adulterants: Canada
germander (Teucrium canadense,
Lamiaceae); germander (T. chamaedrys);
Scutellaria spp., e.g., Alpine
skullcap (S. alpina), Chinese skullcap
(S. baicalensis), hoary skullcap (S. incana), heartleaf skullcap (S. ovata), and marsh skullcap (S. galericulata).1,8
3.2
Sources of information confirming adulteration: The most comprehensive review on
adulteration of skullcap has been published by Foster in HerbalGram for the ABC-AHP-NCNPR Botanical Adulterants Program.2
Other sources for information on skullcap adulteration include the American Herbal
Pharmacopoeia monograph on Scutellaria
lateriflora by Upton et al.,1 and the PhD thesis by Brock.8
Some of the adulteration seems to be due to the sale of mislabeled seed material,
e.g., the inadvertent cultivation of S.
incana in North America, or of S.
ovata in the United Kingdom.1,8 Leroy Ballard, president at Nature’s Cathedral, Inc., an
American grower and supplier of native American medicinal plants, commented
that there are still between 1350 and 1800 kg (3000 and 4000 lbs) of S. incana sold as “Scutellaria spp.” in the United States, but most of this material
is exported overseas. (L. Ballard oral communication to S. Gafner, January 28,
2015). According to Brock, it is not clear how much of the skullcap material
used by herbalists in the UK is actually S.
ovata.8 Further evidence of ongoing adulteration of skullcap products
available in the US market is demonstrated by the results from a study in 2011
by researchers at the United States Department of Agriculture, where 5 out of
13 commercial dietary supplements from US manufacturers purchased on the
Internet were adulterated, reportedly with Canada germander and Chinese skullcap.14
[Note: The original publication does not state the source of the purchased
products, but one of the authors has confirmed that they were from American
(US) manufacturers. (P. Chen e-mail to S. Gafner, September 4, 2015)] Adulteration of commercially sold skullcap
raw material with germander (species not identified) was also reported in 2012
by Walker and Applequist.15 Germander was formerly sold routinely as
a bulk botanical in the United States but it is no longer offered by most
herbal suppliers in the North American market (L. Ballard oral communication to
S. Gafner, January 28, 2015).
3.3
Accidental or intentional adulteration: As indicated above, some of the adulterated material on
the market may be due to rare accidental misidentification when material is
harvested in the wild, or the cultivation of crops where the seeds have been
mislabeled, which is likely the case for some of the adulteration with other
species from the genus Scutellaria
(except adulteration with Chinese skullcap, S.
baicalensis, which does not grow in the same geographical area as S. lateriflora). The reasons behind the
adulteration of skullcap with germander species is a matter of debate. Some
experts suggest that it is accidental, but it is now believed that at least
part of the adulteration is deliberate since the Teucrium species have a
heavier dry weight than skullcap and therefore, a much higher yield is obtained
when harvesting germander (E. Fletcher e-mail to S. Gafner, January 20, 2015; A.
Chandra, e-mail to S. Gafner, January 23, 2015).12,16 Nomenclatural
confusion may also play a role, as pink skullcap is a common name applied to Canada
gemander.2
3.4
Frequency of occurrence:
There is no comprehensive published study on the frequency of skullcap
adulteration. The only study looking at the adulteration of skullcap dietary
supplements included a limited amount of samples (n = 13) from manufacturers in
the United States purchased over the Internet.14 In this study, 38%
of the samples were found to be adulterated. On the other hand, a study looking
at whole or minimally processed skullcap raw materials (n = 10) purchased from
vendors within the United States, did not find any adulterated material,
although the authors of the study specify that they “have
seen a recent sample of commercial skullcap, not included within this study,
that was over 50% Teucrium”.15
Similarly, a study investigating the authenticity of 11 commercial dietary
supplements (10 extracts and one product made with crude powdered material) sold
in the United States, using species-specific DNA primers, concluded that all
nine samples from which DNA was obtained contained S. lateriflora. Two samples, including the product made with
powdered raw herb, did not contain DNA of sufficient quality to determine the
identity of the material (D. Harbaugh Reynaud e-mail to S. Gafner, January 14,
2016). No chemical assays were performed on these samples to confirm the
results.
3.5
Possible safety/therapeutic issues:
Substitution of S.
lateriflora was a
prominent issue in 2002 due to an Australian herbal product’s being implicated
in the death of a patient due to liver failure.17 According to the
label, the herbal product contained kava (Piper
methysticum, Piperaceae), passionflower (Passiflora incarnata, Passifloraceae) and skullcap. The authors of
the case report suggested that the liver failure was possibly due to the
ingestion of kava, a botanical that has been linked to rare occurrences of
liver toxicity.18 However, the causative agent for the death of the
Australian patient was never confirmed. The Australian Therapeutics Goods
Administration (TGA) analyzed the product and determined that it did not
contain skullcap. Some of the known skullcap adulterants, Teucrium species are known to cause
liver injury in humans.19 The hepatotoxicity in Teucrium has been ascribed to the diterpenoid fraction.20
The liver toxicity of germander is influenced by a number of factors, including
diet, the type of germander preparation, and possibly genetic factors.21,22
In contrast to many of the germander neo-clerodane diterpenes, those with a
tetrahydrofuran moiety did not show hepatotoxic effects. The neo-clerodane
diterpenes isolated from skullcap by Bruno et al.23 are different
since they are substituted with either a dihydrofuran-fused tetrahydrofuran
moiety or a fused tetrahydrofuran-γ-lactone ring. The detection of these
specific diterpenes may offer a way to uncover adulteration, although
subsequent studies failed to detect diterpenes in skullcap.24,25
The root of Chinese skullcap (S. baicalensis) is widely used in
Traditional Chinese Medicine. There are some reports of allergic reactions,
diarrhea, and stomach discomfort after ingestion or injection of Chinese skullcap.26
There are also a small number of case reports that have linked Chinese skullcap
to liver injury,27,28 but this implication is based on previous
reports where causality between Chinese skullcap ingestion and liver injury
reportedly has not been established,29 or on case reports
implicating a proprietary mixture of flavonoids from Chinese skullcap,
catechins from betelnut palm (Areca
catechu, Arecaceae), and zinc bisglycinate sold as a medical food under the
brand name Limbrel® (Primus Pharmaceuticals, Phoenix, AZ).28
Aboveground parts of barbed skullcap (S. barbata),
a skullcap species native to China, are similarly used and theoretically could
be substituted for S. lateriflora,
though this has not been formally reported. Since S. lateriflora does not grow naturally in China, and based on current
knowledge, is not generally cultivated there, there is a greater likelihood
that attempts by companies to procure S.
lateriflora from Chinese suppliers could result in use of Chinese species.
The
substitution of skullcap with material from other species of Scutellaria does not pose an apparent
safety risk, although the data on use in humans with the adulterating species is
more limited. Scutellaria galericulata, which is also used in herbal medicine, is believed to have
similar actions and indications as S. lateriflora.16 The ethnobotanical use of S. galericulata and S. incana
in North America is described by Moerman.30 Scutellaria galericulata herb has been used by the Delaware tribe of
Native Americans as a gastrointestinal aid and a laxative. The Ojibwe tribe
used the aboveground parts for heart trouble. Scutellaria incana decoctions were used by the Cherokee as
abortifacient, to treat diarrhea, against breast pain and as a gynecological
aid, but ethnobotanical research suggests that Native American tribes used the
root of the plant rather than the aboveground parts.30 In addition, the
chemical composition of these species, with the exception of the flavonoids,
has not been established in detail.
3.6 Analytical methods to detect adulteration: Confirmation of species identity and
purity may be achieved by organoleptic methods, if conducted by qualified
personnel (e.g., a botanist) for plant material in its whole form. For establishing
the identity of cut or powdered raw material, a combination of a physical
assessment test (e.g., macroscopic or microscopic) with chemical identification
methods or a suitable genetic approach is considered appropriate.
Chromatographic methods, such as high-performance thin-layer chromatography (HPTLC)
and high-performance liquid chromatography (HPLC), can be used for chemical
characterization of raw material and extracts. A comprehensive evaluation of
publicly available methods for the authentication of skullcap and detection of
adulterants in skullcap, the Skullcap Laboratory Guidance Document, is available through the
ABC-AHP-NCNPR Botanical Adulterations Program website.31
3.7 Perspectives: Industry expert Steven Foster believes that “there is no accidental
misidentification of Teucrium canadense
as Scutellaria lateriflora. That is a
myth. One can easily harvest a pick-up truck load of T. canadense in a morning, whereas one would be hard-pressed to
harvest a few pounds of any Scutellaria
spp. from any wild habitat anywhere in the United States in a day. The
adulteration of Scutellaria lateriflora
with Teucrium canadense is pure and
simple ‘under the radar’ economic adulteration.” (S. Foster, e-mail to S.
Gafner, January 28, 2015)
4
Conclusions
Based on a survey in the United
Kingdom,32 skullcap is a highly regarded medicinal herb with herbal
medicine practitioners. It has remained relatively popular in the United States
as a botanical to treat anxiety and stress-related conditions.1 The
substitution of skullcap with germander species is particularly deplorable
because of the known toxicity of species of plants in the genus Teucrium. Such adulteration is easily
detected by a variety of analytical methods, a detailed report of which is
available in the Skullcap Laboratory Guidance Document,31 and as such, the
potentially dangerous presence of Teucrium
material labelled as skullcap in botanical raw materials or finished
products cannot be excused.
5
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Scotts Valley, CA: American Herbal Pharmacopoeia; 2009.
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with American germander. HerbalGram. 2012:(93);34-41. Available at: http://cms.herbalgram.org/herbalgram/issue93/FEAT_skullgerm.html.
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Revision summary
Version # , Author,
|
Date Revised
|
Section Revised
|
List of Changes
|
Version 1,
S. Gafner
|
n/a
|
n/a
|
None
|