Horny Goat Weed/Epimedium

Horny Goat Weed is a common name used to describe Epimedium (Epimedium spp.; Berberidaceae) species, which are perennial, low-growing, herbaceous plants with leathery leaves. The genus Epimedium comprises more than 50 species, most of which are native to China; some species are also found across eastern, southern, and central Asia, and in Europe.

Several Epimedium species have a history of use in traditional Chinese medicine, and some other traditional Asian systems of medicine, for various medical conditions. In China and Japan, E. sagittatum (Siebold & Zucc.) Maxim. has been used to treat impotence, osteoporosis, and hypertension. In Korea, E. koreanum Nakai was also used traditionally for impotence. Today, E. sagittatum, E. koreanum, E. brevicornu Maxim., and E. wushanense T.S.Ying, are accepted as sources of Herba Epimedii by the Chinese Pharmacopoeia.¹

Common names

Horny goat weed, rowdy lamb herb, barrenwort, bishop’s hat, herba epimedii [English]; yin yang huo, yangheye [Chinese]; hozaki-no-ikari-sō [Japanese] and others. [NB: the common name ‘goat weed’ is also used for several other (unrelated) plants].

Preparations

Traditional preparations used the dried aerial parts of Epimedium plants macerated in wine, or decocted in water, for oral consumption.¹ Contemporary preparations in the global market, including New Zealand, include oral dose forms (tablets, capsules, liquid extracts) and topical dose forms (creams), containing extracts of the aerial parts of Epimedium species, formulated as single-ingredient products, or multi-ingredient products containing other herbal and non-herbal ingredients. Some products state they are standardised for content of icariin, a flavonoid compound. In New Zealand, chocolate bars labelled as containing horny goat weed and other herbal ingredients are also available.

Manufacturers’ claims

Products containing Epimedium are promoted as enhancing libido and sexual health for men and women, supporting kidney and adrenal function, improving blood flow, and reducing bone loss in post-menopausal women, among other claims.

Active constituents

The important bioactive compounds of the genus Epimedium – including the species used in ‘natural health’ products – are flavonoids; the major flavonoid compounds include icariin, epimedin A, epimedin B and epimedin C. Other compounds found in species in the genus Epimedium include lignans, ionones, phenol glycosides, phenethyl alcohol glycosides, and sesquiterpenes, among others.¹ The constituent profile of Epimedium varies across different species.

Evidence for efficacy

Preclinical studies have described erectogenic, oestrogenic, anti-osteoporotic, anti-aging, antioxidant, anticancer, antiviral, lipid-lowering, cardioprotective, and hepatoprotective effects of Epimedium, but, at present, there is a lack of clinical evidence to support these activities.²

Clinical research with preparations containing Epimedium has focussed on exploring effects on sexual function, and prevention and treatment of osteoporosis, but there is no definitive evidence of efficacy in these conditions. Large, robust trials are required involving patients sampled from various population groups; studies should report comprehensive descriptions of Epimedium extracts used, including whether the product meets accepted standards for pharmaceutical quality.

Small clinical trials have investigated the effects of different multi-herb products containing extracts of Epimedium species on male sexual function. In a randomised, double-blind, placebo-controlled trial in India, 78 men aged 25–50 years with mild-to-moderate erectile dysfunction received a multi-herb product, VigRX Plus^® (containing Epimedium sagittatum leaf extract 15 mg/capsule and 10 other herbal extracts), or placebo, two capsules twice daily for 12 weeks. Compared with placebo, treatment with the multi-herb product showed a statistically significant increase in the mean International Index of Erectile Function (IIEF) score (20.10 vs 1.0, P < 0.001).³ In a crossover study involving a 1-week washout period, 63 Thai men with mild-to-moderate erectile dysfunction were randomised to receive Cappra^® (a blend of 13 Chinese herbs, including an Epimedium species), or placebo, for 2 weeks. Participants took one tablet approximately 1 h before planned sexual activity, with a minimum of three tablets during the 2-week treatment period. A statistically significant improvement was reported for the mean change in IIEF score from baseline for the erectile function domain for Cappra® recipients compared with placebo recipients (4.87 vs 3.44, P = 0.032). However, mean changes in IIEF scores for other domains (orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction) were not statistically significant.⁴ Both trials had methodological limitations, and the multi-herb product interventions were not adequately described in the clinical trial publications.

A recent systematic review and meta-analysis included 12 randomised controlled trials of single-ingredient preparations of Epimedium involving a total of 1017 middle-aged and older patients with osteoporosis. Seven trials compared Epimedium plus conventional pharmacotherapy with conventional pharmacotherapy alone, and five trials compared Epimedium alone with conventional pharmacotherapy. A meta-analysis of 10 of the trials across both comparisons indicated a significant improvement in bone mineral density in the Epimedium group (SMD = 0.83, 95% CI 0.27–1.40, P = 0.004). Analyses for Epimedium plus conventional pharmacotherapy (SMD = 1.26, 95% CI 0.15–2.37, P = 0.03) and Epimedium alone (SMD = 0.42, 95% CI 0.10–0.74, P = 0.009) showed significant improvement in bone mineral density compared to the respective control groups. Subgroup analyses indicated that the duration of administration of the intervention (≤3 months or >3 months) may impact treatment outcomes. Longer treatment (>3 months) with Epimedium plus conventional pharmacotherapy was associated with more significant benefits for bone mineral density (P = 0.03), while ≤3 months’ treatment with Epimedium alone was more beneficial (P = 0.002).⁵ The evidence from this review is limited as several low-quality studies were included. In these trials, the Epimedium doses varied, and the duration of treatment ranged from 1 to 12 months. Most trials did not provide full details of the Epimedium material tested, including the species and plant part used.

Adverse effects

At present, there are no known safety concerns with Epimedium when consumed at recommended doses, but this is based on limited information. Long-term or excessive use is not recommended.

Epimedium may have androgenic and oestrogenic activity; its use in children and in pregnant and breastfeeding women should be avoided.⁶

Comprehensive investigation of the clinical safety profile of Epimedium, its constituents (such as icariin), and contemporary products, including where used in a pharmaceutical/medicinal context, is required.

Interactions

The potential for preparations of Epimedium to interact with other natural health products and medicines administered concurrently, particularly those with similar or opposing effects, should be considered.

In vitro, an extract of E. brevicornu and icariin (a constituent of E. brevicornu and some other Epimedium species) showed inhibitory activity against phosphodiesterase type-5, although to a lesser extent than did sildenafil.⁷ Thus, based on limited experimental evidence, Epimedium may potentiate the effects of sildenafil, tadalafil and vardenafil; the clinical relevance of this is not known. It is advisable to warn patients of the potential for harm from taking products labelled as containing Epimedium species concurrently with phosphodiesterase type-5 inhibitors.

Similarly, Epimedium may have androgenic and oestrogenic activity; its use in patients with hormone-sensitive conditions, and those taking medicines with androgenic or oestrogenic activity may not be appropriate.