Horny Goat Weed

Abstract

This chapter presents indications, clinical evidence, pre-clinical evidence, mechanisms of action, interactions, and contraindications of Horny Goat Weed (Epimedium spp.). Horny Goat Weed is used to treat sexual dysfunction, particularly impotence in men and lack of libido in women. In traditional Chinese medicine, it is also used widely for osteoporosis. Epimedium species are used to treat a number of other conditions including rheumatic arthritis, menopausal symptoms and memory loss. Adverse effects, dosage, and general plant information are included in the chapter. According to a Chinese legend, a goat herder first noticed the qualities of the plant after he observed far more sexual activity in his goats after they ate it; hence the common name.

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Horny Goat Weed Epimedium spp.
Mainly: E. brevicornu Maxim.; E. koreanum Nakai; E. pubescens Maxim.; E. sagit-
tatum (Siebold & Zucc.) Maxim. Other species of Epimedium are used medicinally,
including E. acunatum Franch and E. wushanense T.S.Ying (as unofcial substitutes
of Epimedii herba)
Synonyms: Aceranthus macrophyllus Blume ex. K.Koch; A. sagittatus Siebold &
Zucc. (=E. sagittatum)
Family: Berberidaceae
Other common names: Barrenwort; bishop’s hat; epimedium; yin yang huo
Drug name: Epimedii herba
Botanical drug used: Aerial parts
Note: Based on the large number of species accepted in the Pharmacopoeia of
China, in combination with the poor information that is generally available about
the quality of products sold as horny goat weed, there can be no evidence-based
use of a product with an acceptable quality. Therefore, it clearly cannot be
recommended by a health care professional.
Indications/uses: To treat sexual dysfunction, particularly impotence in men
and lack of libido in women. In traditional Chinese medicine, it is also used
widely for osteoporosis. Epimedium species are used to treat a number of
other conditions including rheumatic arthritis, menopausal symptoms and
memory loss.
Evidence: There is limited evidence to support the use of epimedium to treat
sexual dysfunction and osteoporosis, although it is known to contain potent
phytoestrogenic compounds.
Safety: Tests in animal models have shown no serious toxicity issues, but human
clinical safety has not been established. Epimedium should not be used con-
currently with other phosphodiesterase-5 (PDE-5) inhibitors, or when PDE-5
inhibitors are contraindicated (e.g. cardiac arrhythmias), or during pregnancy
and lactation.
Main chemical compounds: The main active constituents are the prenylated
avonoids, icariin and its metabolites, epimedins A, B, C, and the sagittatosides.
Phytopharmacy: An evidence-based guide to herbal medicinal products, First Edition.
Sarah E. Edwards, Inês da Costa Rocha, Elizabeth M. Williamson and Michael Heinrich.
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Horny Goat Weed 211
Other active compounds present include avonol glycosides (of kaempferol,
quercetin, myricetin); avones (tricin, luteolin); biavones (gingketin, isogingketin,
bilobetin); lignans such as syringaresinol; alkaloids (e.g. epimediphine from
E. koreanum); β-sitosterol (E. sagittatum,E. brevicornu); and a chalcone, isoliquir-
itigenin (from E. koreanum) (Ma et al. 2011; Pharmaceutical Press Editorial Team
2013; Zhang et al. 2013c).
Clinical evidence:
Sexual dysfunction: Limited clinical data are available on the effects of epimedium
on erectile dysfunction. A small double-blind clinical trial was reported assessing
an epimedium herbal complex supplement in 25 healthy men and 13 men who had
used sildenal (Viagra). The men were administered with the herbal complex for a
minimum of 45 days. Daily use of the epimedium preparation was found to enhance
sexual satisfaction to a greater extent than sildenal (Ma et al. 2011).
Bone health and osteoporosis in menopause: A ve-year follow-up study of a
herbal preparation of epimedium for prevention of postmenopausal osteoporosis
and fragility fractures found that it was able to reduce postmenopausal bone loss,
and also showed some potential for reduction in fragility fracture incidence (Deng
et al. 2012). A randomised, double-blind placebo-controlled clinical study in 85
postmenopausal women with osteopenia (lower than normal mineral bone density,
considered a precursor to osteoporosis), were treated with icariin 60mg, combined
with the isoavonoids daidzein 15 mg, and genistein 3mg, daily for 24 months. All
patients were also given calcium 300 mg daily. A statistically signicant, though
small, increase in bone density was found in the test group and bone resorption
markers were signicantly decreased, compared to the control group (Zhang et al.
2007). Isoavones are oestrogenic and so also have osteogenic activities.
Other oestrogenic effects: A study evaluating the effects of Epimedii herba water
extract on blood lipid and sex hormone levels in 90 postmenopausal women found
that after 6 months of medication, the extract decreased total cholesterol and triglyc-
eride levels (p<0.01) and signicantly increased serum levels of oestradiol, com-
pared with the pre-treatment level (Yan et al. 2008).
Pre-clinical evidence and mechanisms of action:
Sexual dysfunction: Icariin has erectogenic properties in animals, via phosphodi-
esterase type 5 (PDE-5) inhibition, and also neurotrophic effects in vitro and in vivo
(Shindel et al. 2010). A study in male rats found increased sexual behaviour after
treatment with epimedium in combination with four other medicinal plants. How-
ever, individual assessment of the herbs showed no improvement, indicating a pos-
sible synergistic action between them (Zanoli et al. 2008). A study in isolated rabbit
corpus cavernosum (CC) smooth muscle showed that epimedium extracts could
elicit a relaxation effect through activation of multiple targets on NO/cGMP sig-
nalling pathways. The study also found that they potentiated the effects of PDE-5
inhibitors (commonly used for erectile dysfunction), such as sildenal and varde-
nal. The crude extracts were found to have a greater potency than the puried
compounds (Chiu et al. 2006).
Bone health and osteoporosis: Icariin is involved in the regulation of multiple
signalling pathways in osteogenesis, anti-osteoclastogenesis, chondrogenesis, angio-
genesis and inammation. It has been reported to have the potential to be used as

212 Phytopharmacy
a substitute for osteoinductive protein-bone morphogenetic proteins, or to enhance
their therapeutic effects, for bone tissue engineering as well as treatment of osteo-
porosis (Zhang et al. 2013b).
Other relevant effects: Icariin has phytoestrogenic properties and has been shown
to promote the biosynthesis of oestrogen by aromatase (Yang et al. 2013). It reduced
the levels of serum total cholesterol and low-density lipoprotein cholesterol, and
reduced platelet adhesiveness and aggregation in atherosclerotic rabbits, demon-
strating lipid-lowering effects (Zhang et al. 2013a). The alkaloid epimediphine has
anticholinesterase activity (Zhang et al. 2013c), which together with the oestrogenic
effects of other constituents, may support the use for memory enhancement.
Interactions: There is conicting evidence about a possible interaction with other
PDE-5 inhibitors such as sildenal (Viagra). In vitro evidence has suggested that
epimedium potentiates PDE-5 inhibitors (Chiu et al. 2006), but a study of the effects
of E. sagittatum extract on the pharmacokinetics of sildenal demonstrated that the
area under the concentration–time curve of sildenal was signicantly decreased
in groups that received a high dose of epimedium extract, suggesting antagonistic
effects (Hsueh et al. 2013). Co-administration with PDE-5 inhibitors should, there-
fore, be avoided until further information is available.
Another in vitro study found that epimedium is a potent inhibitor of cytochrome
P450 isoforms (including CYP1A2, CYP2C19, CYP2E1, CYP2C9, CYP3A4,
CYP2D6) and NADPH-CYP reductase, indicating a possible potential for inter-
action with other drugs, although the clinical signicance is not known (Liu et al.
2006).
Contraindications: Epimedium should not be used during pregnancy and lacta-
tion as it has oestrogenic activity. Paediatric use is not appropriate. People with heart
conditions should avoid using epimedium and long-term use is not recommended
(Pharmaceutical Press Editorial Team 2013).
Adverse effects: In high doses (not specied), epimedium may have a stimulatory
effect and cause sweating or a feeling of heat. Prolonged use of excessive amounts
in animal studies was associated with decreased thyroid activity (Ma et al. 2011).
A case was reported of a 66-year-old man who developed heart arrhythmia
and hypomania after taking a herbal sexual enhancement product containing
epimedium. As it was a multi-ingredient preparation, and the man was predisposed
to heart disease and possible mood disorder, it is unclear if this was caused by
epimedium or another ingredient (Partin and Pushkin 2004).
Dosage: For products, see manufacturers’ instructions. For the herb, the adult dose
is 3–9 g dried aerial parts daily (Pharmaceutical Press Editorial Team 2013).
General plant information: According to a Chinese legend, a goat herder rst
noticed the qualities of the plant after he observed far more sexual activity in his
goats after they ate it; hence the common name (Ma et al. 2011).
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